Optimize `**/*.EXT` to use `end_with?('.EXT')` over slow `fnmatch?`

What does this MR do and why?

This MR implements an optimization for CI's rules.exists clause **/*.EXT.

Given this example:

eslint-sast:
  extends: .sast-analyzer
  rules:
    - if: $CI_COMMIT_BRANCH
      exists:
        - '**/*.html'
        - '**/*.js'

For large repositories (> 10k files) this clause would always match if the amount of (slow) comparisons (via fnmatch?) would exceed 10k.

Instead of increasing MAX_PATTERN_COMPARISON (#227632) we can use the much faster (24x) end_with? operation.

To protect GitLab.com this optimization is behind a feature flag. See gitlab-com/gl-infra/production#17531 (closed).

Draft?

• Test this performance optimization behind a feature flag or similar
• Adjust documentation
  • No documentation required. See https://docs.gitlab.com/ee/development/feature_flags/#gitlab_com_derisk-type

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