Add labeler action to ease reviews dispatching

[clamoriniere]

What this PR does / why we need it:

Add labeler github action to automatically add labels based on modified files. It should help code review dispatching.

Which issue this PR fixes

(optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged)

• fixes #

Special notes for your reviewer:

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• [ ] Chart Version bumped
• [ ] Documentation has been updated with helm-docs (run: .github/helm-docs.sh)
• [ ] CHANGELOG.md has been updated
• [ ] Variables are documented in the README.md
• [ ] For Datadog Operator chart or value changes update the test baselines (run: make update-test-baselines)