Add Minitest CI integration

[bravehager]

What does this PR do?

Add CI Visibility support for the Minitest framework.

Motivation

Datadog doesn't currently support using Minitest with the CI Visibility feature. It's easy enough to add your own custom integration, but I think it makes sense for dd-trace-rb to provide first-class support for Minitest given that it's the default testing framework for Ruby on Rails.

Additional Notes

• RSpec uses a relative path with the ./ prefix for the test suite name. Right now, we're using Pathname.new(path).relative_path_from(Pathname.pwd).to_s which doesn't include the ./ prefix. Should we mirror the RSpec setup?
• Currently, it only supports minitest/unit, I haven't dug into what it would take to support minitest/spec.
• Minitest supports skip reasons, but provides a default message of "Skipped, no message given". Should we exclude the default message assuming that it doesn't provide much value?

I realize this is a pretty big patch that you might not want to accept from an outside contributor, but I figured I'd put together a PR since we've been using this internally.

How to test the change?

• Added unit tests for instrumentation

[marcotc]

👋 @bravehager, thank you so much for the contribution!

I'm pinging the CI team to get their 👀 here asap.

Thank you again!

[juan-fernandez]

this is great, thanks for this! ❤️

I've tested this end to end with the test suite in https://github.com/freeCodeCamp/devdocs and it works wonderfully.

[bravehager]

Anything I can do to help get this merged? I see there's a CI check blocked but seems resolved by #2929, so might just need a merge or rebase.

[marcotc]

Thank you so much, @bravehager!

[marcotc]

Could you add a section for Minitest documentation, similar to the RSpec one here: https://github.com/DataDog/dd-trace-rb/blob/master/docs/GettingStarted.md#rspec

[codecov-commenter]

Codecov Report

Merging #2932 (9311ef9) into master (18b6322) will decrease coverage by 0.03%.
The diff coverage is 74.73%.

@@            Coverage Diff             @@
##           master    #2932      +/-   ##
==========================================
- Coverage   97.96%   97.93%   -0.03%     
==========================================
  Files        1282     1287       +5     
  Lines       70959    71052      +93     
  Branches     3265     3272       +7     
==========================================
+ Hits        69512    69586      +74     
- Misses       1447     1466      +19     

Impacted Files	Coverage Δ
lib/datadog/ci/contrib/minitest/test_helper.rb	35.71% <35.71%> (ø)
lib/datadog/ci/contrib/minitest/patcher.rb	84.61% <84.61%> (ø)
lib/datadog/ci/contrib/minitest/integration.rb	87.50% <87.50%> (ø)
...adog/ci/contrib/minitest/configuration/settings.rb	94.11% <94.11%> (ø)
lib/datadog/ci.rb	100.00% <100.00%> (ø)
lib/datadog/ci/contrib/minitest/ext.rb	100.00% <100.00%> (ø)

... and 4 files with indirect coverage changes

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[marcotc]

Thank you so much for the documentation!

I noticed one last thing: we have rbs type signatures in the repository and check them with steep. I noticed there's a type checking failure in the PR (Check / Check types): https://github.com/DataDog/dd-trace-rb/actions/runs/5427100107/jobs/9930832333?pr=2932

Could you follow the steps in the failure output and see if you can address it. If you find that the guide referenced there is insufficient please let us know so we can improve it.