Run e2e tests during mergequeue for `datadog` chart

[clamoriniere]

What this PR does / why we need it:

• Run e2e tests during mergequeue only for datadog chart
• Don't run e2e tests for any other charts change on main: for now e2e tests is only testing the datadog chart.
• Keep the possibility to run e2e test manually on other branch.

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)

[clamoriniere]

/merge

[dd-devflow[bot]]

:steam_locomotive: MergeQueue

Pull request added to the queue.

This build is going to start soon! (estimated merge in less than 0s)

Use /merge -c to cancel this operation!

[clamoriniere]

/merge --cancel

[dd-devflow[bot]]

:warning: MergeQueue

This merge request build was cancelled

If you need support, contact us on Slack #ci-interfaces!

[clamoriniere]

I tried but I still see the e2e test job in the gitlab ci