Add image parameters to compose.yaml

[tgeoghegan]

Compose files can be parameterized using Bash-style (sigh) syntax (1). We add variables JANUS_AGGREGATOR_IMAGE, JANUS_MIGRATOR_IMAGE, DIVVIUP_API_IMAGE and DIVVIUP_API_MIGRATOR_IMAGE to allow setting Docker image tags like so:

DIVVIUP_API_IMAGE=myrepository.dev/divviup_api:0.0.1 \
  JANUS_AGGREGATOR_IMAGE=myrepository.dev/janus_aggregator:0.7.8 \
  docker compose up

These variables are interpolated into the image field of the service elements (2). Because we also have a build element on the divviup-api services, the behavior is to pull the specified image and fall back to the build element if it can't be found (3). So if you want to build divviup-api from source and use that, do:

DIVVIUP_API_IMAGE=divviup_api:1 docker compose up

divviup_api:1 will be built from the local context, unless it's already in the local Docker repository, and then launched.

We provide defaults for all these images that pull from Divvi Up owned public artifact repositories. It's somewhat unfortunate that we use a divviup-api version that is behind main, but on the other hand the objective is to enable a demo experience, so it makes sense to pin Janus and divviup-api versions where the demo is known to work end-to-end.

[tgeoghegan]

This PR isn't quite ready to go, because the default image here is not in a public repository. I'm working on separate changes to enable docker-release.yml to push to us-west2-docker.pkg.dev/divviup-artifacts-public and will update this URL to point there before merging this.

[divergentdave]

I think an easier entry point would be to create another file, compose.dev.yaml, and use include or extends to import parts of an end-user-focused compose.yaml. The dev file could then use image: !reset null to ensure it builds from source, without requiring the user to make up image names.

[tgeoghegan]

Seems reasonable! The simplest thing would be to use merge, but that requires passing multiple compose YAMLs in the correct order at the command line so that merge rules are evaluated correctly (i.e., docker compose -f compose.yaml -f compose.dev.yaml up works, but docker compose -f compose.dev.yaml -f compose.yaml up does not).

So I opted for include. This requires us to add a further overrides file, but it makes the dev setup easier to use.

I also moved the build stanzas to compose.dev.yaml, on the premise that this makes the behavior of compose.yaml less surprising: if someone is using compose.yaml and makes a typo in an image name, I think we want them to get a clear docker pull error rather than have an image with that tag "silently" get built.

[divergentdave]

Unfortunately, Dependabot cannot update image names in compose.yaml for us: dependabot/dependabot-core#390. We could maybe add a GitHub Actions workflow that runs sed and pushes a commit after a release.

[divergentdave]

The develop stanzas are mixed up, this one should go on divviup_api_migration and vice versa.

[tgeoghegan]

Still need #1093 and in turn https://github.com/divviup/janus-ops/pull/1825 before I can merge this.