[CIVIS-2844] Test suites support

[anmarchenko]

What does this PR do?
This PR adds support for test suites when test suite level visibility is enabled and a manual API to trace it.

To start a test suite:

Datadog::CI.start_test_suite(test_suite_name)

To get an active test suite and finish it:

test_suite = Datadog::CI.active_test_suite(test_suite_name)
test_suite.passed!
test_suite.finish

It supports running multiple test suites in parallel inside a process.

How to test the change?
Gist for testing:
https://gist.github.com/anmarchenko/b58ebb39fe2f9e391344d7d66212e3da

Produces the following session trace:

[codecov-commenter]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (c42591d) 99.34% compared to head (bf6bea8) 99.29%.

Files	Patch %	Lines
spec/datadog/ci/context/global_spec.rb	95.52%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #77      +/-   ##
==========================================
- Coverage   99.34%   99.29%   -0.05%     
==========================================
  Files         131      135       +4     
  Lines        4754     5140     +386     
  Branches      166      171       +5     
==========================================
+ Hits         4723     5104     +381     
- Misses         31       36       +5     

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