ci: Split the release image builds into individual workflows #805
Description
Much the same as was done for the dev workflows in #733
- Keeps release builds as similar as possible to dev builds
- Reuses custom actions to abstract detail from the workflow
Acceptance:
- Can do test runs of release image builds
- Reuse custom actions (adapt where required so they work for both dev and release)
- Add status badges to README.md (like for dev, using the script to generate them)