[receiver/dockerstats] remove old scraper implementation

[jamesmoessis]

Something bad happened to the commit history when I was resolving conflicts over on #18019, so I thought it's better to start fresh here.

Description:

• Removes old implementation that featuregate toggled (keeps featuregate as discussed)
• Removes deprecated config option provide_per_core_cpu_metrics
• There's no new code. Any green lines are things that I shuffled around so everything is in receiver.go (removed metrics.go and receiver_v2.go).

Link to tracking Issue: Closes #9794

Testing:
No behaviour changes. Same metrics are still produced, and this is validated by existing tests.

Documentation:
Updated README.

[runforesight]

Foresight Summary

    
Major Impacts

build-and-test-windows duration(5 seconds) has decreased 40 minutes 27 seconds compared to main branch avg(40 minutes 32 seconds).

View More Details

⭕  build-and-test-windows workflow has finished in 5 seconds (40 minutes 27 seconds less than main branch avg.) and finished at 8th Feb, 2023.

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Job	Failed Steps	Tests
windows-unittest-matrix	-     🔗	N/A	See Details
windows-unittest	-     🔗	N/A	See Details

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✅  telemetrygen workflow has finished in 1 minute 3 seconds (1 minute 57 seconds less than main branch avg.) and finished at 8th Feb, 2023.

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Job	Failed Steps	Tests
build-dev	-     🔗	N/A	See Details
publish-latest	-     🔗	N/A	See Details
publish-stable	-     🔗	N/A	See Details

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✅  check-links workflow has finished in 1 minute 29 seconds (1 minute 4 seconds less than main branch avg.) and finished at 8th Feb, 2023.

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changed files	-     🔗	N/A	See Details
check-links	-     🔗	N/A	See Details

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✅  changelog workflow has finished in 1 minute 42 seconds and finished at 8th Feb, 2023.

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changelog	-     🔗	N/A	See Details

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✅  prometheus-compliance-tests workflow has finished in 3 minutes 12 seconds (5 minutes 20 seconds less than main branch avg.) and finished at 8th Feb, 2023.

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Job	Failed Steps	Tests
prometheus-compliance-tests	-     🔗	✅ 21  ❌ 0  ⏭ 0    🔗	See Details

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✅  build-and-test workflow has finished in 37 minutes 47 seconds (20 minutes 7 seconds less than main branch avg.) and finished at 8th Feb, 2023.

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Job	Failed Steps	Tests
unittest-matrix (1.18, internal)	-     🔗	✅ 561  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, internal)	-     🔗	✅ 561  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, processor)	-     🔗	✅ 1472  ❌ 0  ⏭ 0    🔗	See Details
correctness-metrics	-     🔗	✅ 2  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.18, processor)	-     🔗	✅ 1472  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, extension)	-     🔗	✅ 546  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.18, extension)	-     🔗	✅ 546  ❌ 0  ⏭ 0    🔗	See Details
correctness-traces	-     🔗	✅ 17  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.18, receiver-0)	-     🔗	✅ 2574  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, receiver-0)	-     🔗	✅ 2574  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.18, exporter)	-     🔗	✅ 2444  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, exporter)	-     🔗	✅ 2444  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.18, receiver-1)	-     🔗	✅ 1958  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, receiver-1)	-     🔗	✅ 1958  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.18, other)	-     🔗	✅ 4673  ❌ 0  ⏭ 0    🔗	See Details
integration-tests	-     🔗	✅ 55  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, other)	-     🔗	✅ 4673  ❌ 0  ⏭ 0    🔗	See Details
setup-environment	-     🔗	N/A	See Details
check-collector-module-version	-     🔗	N/A	See Details
check-codeowners	-     🔗	N/A	See Details
checks	-     🔗	N/A	See Details
build-examples	-     🔗	N/A	See Details
lint-matrix (receiver-0)	-     🔗	N/A	See Details
lint-matrix (receiver-1)	-     🔗	N/A	See Details
lint-matrix (processor)	-     🔗	N/A	See Details
lint-matrix (exporter)	-     🔗	N/A	See Details
lint-matrix (extension)	-     🔗	N/A	See Details
lint-matrix (internal)	-     🔗	N/A	See Details
lint-matrix (other)	-     🔗	N/A	See Details
lint	-     🔗	N/A	See Details
unittest (1.19)	-     🔗	N/A	See Details
unittest (1.18)	-     🔗	N/A	See Details
cross-compile (darwin, amd64)	-     🔗	N/A	See Details
cross-compile (darwin, arm64)	-     🔗	N/A	See Details
cross-compile (linux, 386)	-     🔗	N/A	See Details
cross-compile (linux, amd64)	-     🔗	N/A	See Details
cross-compile (linux, arm)	-     🔗	N/A	See Details
cross-compile (linux, arm64)	-     🔗	N/A	See Details
cross-compile (linux, ppc64le)	-     🔗	N/A	See Details
cross-compile (windows, 386)	-     🔗	N/A	See Details
cross-compile (windows, amd64)	-     🔗	N/A	See Details
build-package (deb)	-     🔗	N/A	See Details
build-package (rpm)	-     🔗	N/A	See Details
windows-msi	-     🔗	N/A	See Details
publish-check	-     🔗	N/A	See Details
publish-dev	-     🔗	N/A	See Details
publish-stable	-     🔗	N/A	See Details

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✅  load-tests workflow has finished in 8 minutes 15 seconds (8 minutes 18 seconds less than main branch avg.) and finished at 8th Feb, 2023.

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Job	Failed Steps	Tests
loadtest (TestIdleMode)	-     🔗	✅ 1  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestTraceAttributesProcessor)	-     🔗	✅ 3  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestMetric10kDPS|TestMetricsFromFile)	-     🔗	✅ 6  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestTraceBallast1kSPSWithAttrs|TestTraceBallast1kSPSAddAttrs)	-     🔗	✅ 10  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestMetricResourceProcessor|TestTrace10kSPS)	-     🔗	✅ 12  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestTraceNoBackend10kSPS|TestTrace1kSPSWithAttrs)	-     🔗	✅ 8  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestBallastMemory|TestLog10kDPS)	-     🔗	✅ 19  ❌ 0  ⏭ 0    🔗	See Details
setup-environment	-     🔗	N/A	See Details

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✅  e2e-tests workflow has finished in 11 minutes 12 seconds (11 minutes 16 seconds less than main branch avg.) and finished at 8th Feb, 2023.

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Job	Failed Steps	Tests
kubernetes-test	-     🔗	N/A	See Details

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[jamesmoessis]

cc @mx-psi @MovieStoreGuy sorry, the #18019 commit history got messed up, so I've re-raised here.

I have kept the initialisation of the featuregate as discussed, and I believe there were no other items to address.

The change is now an "enhancement" instead of "breaking" because all behaviour still the same. It's still a breaking change because I removed the deprecated config option.