[SDTEST-160] API metrics

[anmarchenko]

What does this PR do? Adds the following metrics:

• git_requests.search_commits
• git_requests.search_commits_ms
• git_requests.search_commits_errors
• git_requests.objects_pack
• git_requests.objects_pack_ms
• git_requests.objects_pack_errors
• git_requests.objects_pack_bytes
• git_requests.objects_pack_files
• git_requests.settings
• git_requests.settings_ms
• git_requests.settings_errors
• git_requests.settings_response
• itr_skippable_tests.request
• itr_skippable_tests.request_ms
• itr_skippable_tests.request_errors
• itr_skippable_tests.response_bytes
• itr_skippable_tests.response_tests

How to test the change? Unit tests are provided

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 98.78049% with 2 lines in your changes missing coverage. Please review.

Project coverage is 98.84%. Comparing base (1ab2fd2) to head (b67a64f).

Files	Patch %	Lines
lib/datadog/ci/transport/http.rb	85.71%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #206 +/- ## ========================================== + Coverage 98.83% 98.84% +0.01% ========================================== Files 251 251 Lines 11416 11526 +110 Branches 509 516 +7 ========================================== + Hits 11283 11393 +110 Misses 133 133 ```

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