Build docker image that can produce signals for a single repository.

[calebbrown]

To make it easy for users, and to facility scenarios where a "one shot" for a single repository is needed for collecting signals and scoring them, add, publish, and maintain a docker image.

Someone can then score a repo with a single Docker command, or a GitHub Action may be used to create signals/scores on the fly.

[mde-gb]

It's currently required to get the whole go development chain up and running to use this tool. Such a docker image would help a lot.