Build contributed recipes in PRs

[mathbunnyru]

Describe your changes

Issue ticket if applicable

Checklist (especially for first-time contributors)

• I have performed a self-review of my code
• If it is a core feature, I have added thorough tests
• I will try not to use force-push to make the review process easier for reviewers
• I have updated the documentation for significant changes

[mathbunnyru]

The idea behind this PR is to be able to build contributed recipes right in PRs if images change.
There is some work that needs to be done in docker.yml to make this work, so I'm going to merge this one as is, and then work on it.
And right now builds are failing, so I can't actually test this easily.