Ability to tag metadata to the docker image

[makeittotop]

Not sure if there is already an option to hand-craft the docker image build name with chosen metadata (example: deployment 'track', version etc) in which case this is probably not needed.

Else it'd be good to differentiate between different images to help perform certain administrative actions.

[rhs]

There isn't any such ability currently, but we could certainly add some flexibility here.

The way forge works depends on being able to deterministically compute the image name based on a hash of all the input sources. You can think of this as an automatically computed "implementation version" (as opposed to a semantic API version). This hash needs to be part of the image name in order for forge to be able to cache docker builds, but we could certainly have a component of the image name that is customizable.

I could also add the ability to add custom labels to docker images. That might be a good place to put some of that information as well.

[tristanpemble]

This is, now that I think about it, kind of increasingly important now that #33 is implemented. Now that you can change the build config depending on environment variables, you can end up with different images with the same project checksum.

Maybe something like:

containers:
  - dockerfile: ./Dockerfile
    tag: {{version}}{%if env.DEBUG %}-debug{% endif %}

With a validation that {{version}} is included in the tag