Add pro:docker option

[kminehart]

This effectively moves what is in pipelines/pro_image.go from this PR into the declarative model that was added here.

Some external projects still depend on that old command so those need to be updated before the pro_image.go pipeline and pro-image commands can be removed.

The benefit of using the declarative model in this case is that we can build the pro image along with every other artifact, and they will reuse the same cloned repositories, compiled frontend, etc.

Example:

dagger run go run ./cmd artifacts -a enterprise:linux/adm64:targz pro:linux/amd64:deb pro:linux/amd64:docker

Because they both use the same compiled frontend, it'll only be compiled once and reused for all artifacts.

And because the pro docker image depends on the pro deb, the pro deb will be built first and given to the pro docker image.

Requirements

The main branch of grafana-build should be compatible with all active versions of Grafana and Grafana-Enterprise.

• I have tested this against main in Grafana.
• I have tested this against main in Grafana Enterprise.
• I have tested this against all active version branches of Grafana (v10.0.x, v10.1.x, v10.2.x, etc).
• I have tested this against all active version branches of Grafana Enterprise (v10.0.x, v10.1.x, v10.2.x, etc).

I also tested the docker artifacts with the --verify command (and with the Dockerfile in this project). Everything looks good!