feat(flatpak-builder): Allow configurable build/repo/state dirs

[Zeglius]

Previously, the flatpak-builder action used hardcoded directories for the build output, local repository, and build state. This change introduces new input parameters to make these directories configurable:

• 'build-dir': Specifies the directory for the application build output.
• 'repo-name': Specifies the directory for the flatpak repository.
• 'state-dir': Specifies the directory to store the build cache.

This flexibility is crucial for environments like GitHub Actions, where default working directories might have limited space. By allowing users to specify paths, they can leverage volume mountpoints (e.g., /mnt) that offer more disk space, preventing "running out of space" errors during the build process.

[Zeglius]

An example of use would be:

jobs:
  flatpak:
    name: "Flatpak"
    runs-on: ubuntu-latest
    container:
      image: ghcr.io/flathub-infra/flatpak-github-actions:gnome-48
      options: --privileged
      volumes:
        - /mnt/flatpak_workflow:/mnt/flatpak_workflow
    steps:
    - uses: actions/checkout@v4
    - uses: flatpak/flatpak-github-actions/flatpak-builder@v6
      with:
        bundle: palette.flatpak
        manifest-path: org.gnome.zbrown.Palette.yml
        cache-key: flatpak-builder-${{ github.sha }}
        build-dir: /mnt/flatpak_workflow/build-dir
        repo-name: /mnt/flatpak_workflow/repo
        state-dir: /mnt/flatpak_workflow/.flatpak-builder

[bilelmoussaoui]

When i tested your patch at bilelmoussaoui/ashpd#322 i get the same limited space error (see https://github.com/bilelmoussaoui/ashpd/actions/runs/20575989270), any clues?

[Zeglius]

When i tested your patch at bilelmoussaoui/ashpd#322 i get the same limited space error (see bilelmoussaoui/ashpd/actions/runs/20575989270), any clues?

You forgot to mount a host volume, should be like this:

    container:
      # ...
      volumes:
        - /mnt/<whatever>:/mnt/<whatever>

The point of this PR was to allow using the hosts /mnt for the cache, which, for some reason, has a lot of free space in Github runners.
Without that volumes param, you will just end up using the default partition (roughly under /home (?), not exaclty sure) and more likely filling it up.