test_file_finder: Use test lists for some sources and add lefthook command

What does this MR do and why?

This MR refactors tests.yml to use test lists in some sources to avoid duplication.

This feature was introduced back in gitlab-org/ruby/gems/test_file_finder!30 (merged). See also gitlab-org/ruby/gems/test_file_finder!30 (comment 1403315578).

This MR also removes references to lib/gitlab/usage_data_counters/known_events/*.yml because this directory was removed in !127588 (merged).

Lastly, this MR also adds lefthook hooks to run scripts/verify-tff-mapping in pre-commit and pre-push.

Screenshots

pre-commit	pre-push

How to verify locally?

scripts/verify-tff-mapping
tff mapping verification passed.

This job also runs on CI!

MR acceptance checklist

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