Add log splitter for CI rspec failed examples

What does this MR do?

• Adds log splitter from this blogpost (section Change #3 — Extracting logs from failed tests) - https://building.buildkite.com/5-ways-weve-improved-flakey-test-debugging-4b3cfb9f27c8#f03c (gist - https://gist.github.com/keithpitt/74950281d01b11bac7b076fb1d3eda1a)
• Example of artifact in this failed job - https://gitlab.com/innerwhisper/gitlab-ce/-/jobs/31416936 (directory log/test)

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

It helps to work:

• with flaky tests: with it we can catch errors in test environment logs
• with any failed specs: we can analyze them using CI artifacts

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

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