Reworked service labeler to act in more cases

[melinath]

Specifically, if labels are removed or if the first comment is edited - but only if there is not a service label yet.

New or Affected Resource(s)

google_alloydb_instance

[github-actions]

** WARNING **: This repository is generated by https://github.com/GoogleCloudPlatform/magic-modules. Any changes made directly to this repository will likely be overwritten. If you have further questions, please feel free to ping your reviewer or, internal employees, reach out to one of the engineers. Thank you!

[melinath]

I'm not entirely sure whether this will work as desired... I'll need to double-check after merge.

[melinath]

Successfully detected existing service label: https://github.com/hashicorp/terraform-provider-google/actions/runs/8606506951/job/23585089624?pr=17794

[melinath]

Successfully computed new service labels: https://github.com/hashicorp/terraform-provider-google/actions/runs/8606515668/job/23585111965?pr=17794#step:5:16 - wasn't able to update because PRs only get read permissions.

[github-actions]

I'm going to lock this pull request because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.
If you have found a problem that seems related to this change, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.