[Infra updates] Build and push a Docker image for the model

[jeancochrane]

For the first step in the new model deployment pipeline described in https://github.com/ccao-data/model-res-avm/pull/21/files, we need to containerize our model code by building a Docker image for the model and pushing it to the GitHub container registry. There are a couple steps required for this:

1. Define a Dockerfile that encapsulates the code and the environment necessary to run the model
2. Define a new GitHub Actions workflow that authenticates with the container registry, checks if the image has changed, and pushes it to the container registry if it has
   1. It might be useful to use Docker's official composite actions for these operations

We'll also want to enable layer caching for the build; see this Docker guide for instructions. I don't think we'll need a cache key, since I think Docker layer caching should take care of that for us automatically, but if we do it should be enough to use dvc.lock.

Some of this work has already been sketched out in code available on GitLab: https://gitlab.com/ccao-data-science---modeling/models/ccao_res_avm/-/blob/master/.gitlab-ci.yml?ref_type=heads