Set OCI annotation labels for better integration with dependency management tools

[mpgirro]

Is your feature request related to a problem? Please describe

The Docker images do not provide Open Container Image annotations in the form of Dockers label. Therefore, tools like Dependabot and Renovate are not able to show release notes or changelog entries when opening PRs for dependency updates.

Describe the solution you'd like

Set org.opencontainers.image.* labels in the Dockerfiles. Especially, the org.opencontainers.image.source label with the URL of this repo as the value. We then enable these tools to fetch the information that is being published with new releases, improving the integration of the images with existing and widely used dependency management tools.

Describe alternatives you've considered

Alternatively, we could use the docker/metadata-action to extra information from the GitHub repository and add it in another step to the build process. This would be very easy if this repo would use the docker/build-publish action. But since the CI workflow is using custom code instead, is much easier to simply set the labels in the Dockerfile.

Additional context

Renovate Documentation on how changelog entries are fetched: https://docs.renovatebot.com/modules/datasource/docker/

I've also opened an issue and a PR for the portainer server for the same request in this image. There, already some labels are set, but the source label is missing. Here, no OCI annotation labels are set yet, therefore at least the same as in the portainer server should set.