Add wrapper action for PR labeler

[devtobi]

The refarch templates provide tooling for project organization via the "PR labeler" functionality.
Currently we have a direct reference to this action but would like to get rid of it via centralization into a custom action.

See https://github.com/it-at-m/refarch-templates/blob/main/.github/workflows/pr_labeler.yaml for our current configuration.
See https://github.com/actions/labeler the documentation of the action itself.