Add check for missing license headers

[mjwolf]

Add make check_license_headers as a test workflow step, in order to detect any yaml or py files without the required license header.

• Have you signed the contributor license agreement? y
• Have you followed the contributor guidelines? y
• For proposing substantial changes or additions to the schema, have you reviewed the RFC process? n/a
• If submitting code/script changes, have you verified all tests pass locally using make test? y
• If submitting schema/fields updates, have you generated new artifacts by running make and committed those changes? n/a
• Is your pull request against main? Unless there is a good reason otherwise, we prefer pull requests against main and will backport as needed. y
• Have you added an entry to the CHANGELOG.next.md? n/a

[stbischof]

https://github.com/marketplace/actions/license-eye-header

You may want to use this ci task

[stbischof]

@mjwolf

Would be also nice if you not just check for

Licensed to Elasticsearch B.V.

But also check fot the Apache License

If its okay, i can do a pr with the ci Plugin. This way we can see this an an extra check in the pr

[mjwolf]

@mjwolf

Would be also nice if you not just check for

Licensed to Elasticsearch B.V.

But also check fot the Apache License

If its okay, i can do a pr with the ci Plugin. This way we can see this an an extra check in the pr

Hi @stbischof, if you'd like to create another PR for this, I'd appreciate it