internal/civisibility: adds the new vcpu_count metric for tslv events

[tonyredondo]

What does this PR do?

This PR adds the new _dd.host.vcpu_count metric to all test suite level visibility events.

Motivation

This new tag will be used by the backend to do some calculations.

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.
• Add an appropriate team label so this PR gets put in the right place for the release notes.
• Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.

Unsure? Have a question? Request a review!

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-09-20 10:02:59

Comparing candidate commit e5d6ee5 in PR branch tony/civisibility-add-vcpucount-tag with baseline commit 054d19d in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 59 metrics, 0 unstable metrics.