feat: set "destination" context for "mongodb" instrumentation

[trentm]

Fixes #1892

[trentm]

Current status: just a first pass.

TODOs:

• test case
• More robust/defensive handling of the event.address etc.

[apmmachine]

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Build stats

• Build Cause: Pull request #1893 updated

• Start Time: 2020-11-26T00:51:20.523+0000

• Duration: 14 min 17 sec

Test stats 🧪

Test	Results
Failed	0
Passed	16398
Skipped	0
Total	16398

[trentm]

TAV test run for me:

% TAV=mongodb ./node_modules/.bin/tav --compat
Testing compatibility with mongodb:
✔ 3.6.3
✔ 3.6.2
✔ 3.5.11
✔ 3.6.1
✔ 3.6.0
✔ 3.5.10
✔ 3.5.9
✔ 3.5.8
✔ 3.5.7
✔ 3.5.6
✔ 3.5.5
✔ 3.5.4
✔ 3.5.3
✔ 3.5.2
✔ 3.5.1
✔ 3.5.0
✔ 3.4.1
✔ 3.4.0
✔ 3.3.5
✔ 3.3.4
✔ 3.3.3
✔ 3.3.2
✔ 3.3.1
✔ 3.3.0

[astorm]

code and concepts look solid and reflect what we discovered about this in slack today. Soft approving, presuming that the lint and ci pass.

[astorm]

Capturing an online conversation here -- both the docs and some spot checking of a port-less mongo connection (mongoose.connect('mongodb://localhost/myapp', {useNewUrlParser: true});) indicate that the address/connection ID will be normalized to include a port, even if the client is configured without one. If somehow a portless address does end up in there, we won't hard fail as exec won't match and the conditional will fail.