CI/Linux: Build/publish Docker images used to create DEB packages

[guihkx]

From now on, whenever we detect a modification to any of the 'ubuntu-*' Dockerfiles in the 'Dockerfiles' directory, a new image will be built first (with 'docker build'), and only then it will be used to actually build the app and generate DEB packages.

If no changes to these Dockerfiles are detected, we'll simply 'docker pull' the already-existing image from the GitHub Container Registry to build the app, which will give us a faster build time.

This new approach allows us to immediately test changes made to these Dockerfiles, without having to first build them locally, test them, push them to an OCI registry, and only then use them on GitHub Actions.

Please note that these images will only be pushed to the GitHub Container Registry if all three conditions below are met:

• We are not on a pull request
• We are on the master branch
• We are on the 'nuttyartist/notes' repository

@nuttyartist If this gets merged, hopefully you don't have to do anything else and the images will automatically published to this page: https://github.com/nuttyartist/notes/pkgs/container/notes

If you guys like this idea, I can do the same for the RPM and AppImage build jobs next.

[guihkx]

I've tested the resulting DEB packages by installing and running them using podman on clean container images of their respective distributions:

• Ubuntu 20.04 (command used: podman run --rm -e DISPLAY -v $XAUTHORITY:/root/.Xauthority:ro -v /tmp/.X11-unix:/tmp/.X11-unix -v ./notes_20.04.deb:/notes.deb ubuntu:20.04 bash -c 'apt-get update && apt-get install -y /notes.deb && notes')

  Screenshot

  

• Ubuntu 22.04 (command used: podman run --rm -e DISPLAY -v $XAUTHORITY:/root/.Xauthority:ro -v /tmp/.X11-unix:/tmp/.X11-unix -v ./notes_22.04.deb:/notes.deb ubuntu:22.04 bash -c 'apt-get update && apt-get install -y /notes.deb && notes')

  Screenshot

  

• Ubuntu 23.10 (command used: podman run --rm -e DISPLAY -v $XAUTHORITY:/root/.Xauthority:ro -v /tmp/.X11-unix:/tmp/.X11-unix -v ./notes_23.10.deb:/notes.deb ubuntu:23.10 bash -c 'apt-get update && apt-get install -y /notes.deb && notes')

  Screenshot

  

[nuttyartist]

That's really great, @guihkx. Thanks!

If you guys like this idea, I can do the same for the RPM and AppImage build jobs next.

Yes, that would be awesome.

[guihkx]

v2 changes (final):

• Updated the Build, package and lint build step to also mount the $GITHUB_OUTPUT file inside the container, so we can set variables useful for GitHub Actions from there.
• Moved the Grab deb package name build step into the Dockerfiles/ubuntu_deb_entrypoint.sh build script.
• Removed leftover FIXME comments.
• Added useful comments to Dockerfiles explaining that you must mount the current git tree into the /src directory inside the container.