Flathub trigger & version check

[wvengen]

The Flathub application source has just moved to using Github Actions to create a new version with all the dependencies. This can be triggered automatically from this repository when a new release is published. Flathub documentation on the trigger. The dispatch action needs a token for access to both the Artisan and Flathub repository (I would suggest a fine-grained access token).

And to make sure the metainfo file is updated on releasing a new version: a check when a new version tag is created.

I haven't ran the actions in practice on the repository, so it could be that something unexpected is encountered. But if it works, it will reduce time for maintainers of both Artisan and the Flatpak.

[MAKOMO]

Wow! Thank you for all your work on this. As I understand, this needs some further configuration on my behalf like creating and adding a token. Could you possible support me on this or just do this yourself? You should already be a developer with read/write access to this repository. Let me know if you need more or if I should take action.

[wvengen]

Thank you for merging this! I'll set up the token.

[wvengen]

Ah, I see now that I need to add an exception for the continuous release :) Will do so directly on the repository.

[MAKOMO]

Excellent! Thanks for your support on this and beyond!

[wvengen]

Unfortunately, I am not able to create a fine-grained access token scoped to both this and the application's Flathub repository. I am not open to creating a personal access token that has access to all my (public) repositories. So I'll remove the Flathub workflow again, and resort to manually triggering the update after a release (can be done from the Github Actions screen there).

When Github supports using fine-grained access tokens here, this can be reconsidered.