Create docker-image.yml

[zerogro42]

Summary

Provide a general description of the code changes in your pull
request... were there any bugs you had fixed? If so, mention them. If
these bugs have open GitHub issues, be sure to tag them here as well,
to keep the conversation linked together.

Other Information

If there's anything else that's important and relevant to your pull
request, mention that information here. This could include
benchmarks, or other information.

If you are updating CHANGELOG.md file or are asked to update it by reviewers,
please add the changelog entry at the top of the file.

Thanks for contributing to Doorkeeper project!

[nbulaj]

Hello @zerogro42 . Any more details about the PR? What it does and why do we need it?

[ThisIsMissEm]

@nbulaj this looks AI generated for some reason. That said, we probably do want a CI/CD workflow that builds the docker image and runs it, considering that's how tests can be run for some folks (and running on host machine fails). I have had a few people mention we should use devcontainers instead, but I'm not sure how that'd work, because my understanding is that we need to install a gemfile (gemfiles/*.gemfile) first before running the tests, so it'll be a slow feedback cycle anyway, and rebuilding the container from scratch might just be easier — but I don't know a lot about devcontainers.