Build InvenioRDM docker images using GitHub Actions

[mfenner]

Description

Adding a GitHub Action that builds the InvenioRDM and Invenio-Nginx Docker images. They can be used to quickly start up InvenioRDM for local development (more work on SSL termination is needed before these images can be used in production). Using an AlmaLinux9 base image. Closes #238.

Checklist

Ticks in all boxes and 🟢 on all GitHub actions status checks are required to merge:

• [x] I'm aware of the code of conduct.
• [x] I've created logical separate commits and followed the commit message format.
• [x] I've added relevant test cases.
• [x] I've added relevant documentation.
• [x] I've marked translation strings (for relevant code).
• [x] I've followed the CSS/JS and React guidelines (for relevant code).
• [x] I've followed the web accessibility guidelines (for relevant code).
• [x] I've followed the user interface guidelines (for relevant code).
• [x] I've identified the copyright holder(s) and updated copyright headers for touched files (>15 lines contributions).
• [x] I've NOT included third-party code (copy/pasted source code or new dependencies).