Added automatic build of Bottles in beta

[Kinsteen]

I copied the manifest file from master, adding the x-checker-data to track the latest commit. It should also auto-merge PRs that the bot creates, only for the beta branch.

This should enable flathub-beta version of Bottles to follow the main branch of the repository, making bleeding-edge fixes available easily for users.

[flathubbot]

Started test build 12887

[flathubbot]

Build 12887 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/125316/com.usebottles.bottles.flatpakref

[flathubbot]

Started test build 12893

[flathubbot]

Build 12893 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/125322/com.usebottles.bottles.flatpakref

[TheEvilSkeleton]

This won't work, because Flathub only checks the main branch (in this case master). What we'll need to do instead is to disable Flathub's data-checker and rely on GitHub Workflow. You can use this as an example: https://github.com/flathub/com.microsoft.Edge/blob/818ad8268a025a0b65fe9a0847fc88a753550ef4/.github/workflows/update.yaml

[flathubbot]

Started test build 12909

[Kinsteen]

This should work, it will run the CI each hour (so the repo will be updated in maximum two hours after a commit in the Bottles repository)

We can let the Flathub bot run on master, and use Github Actions only for the beta branch

[flathubbot]

Build 12909 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/125338/com.usebottles.bottles.flatpakref

[TheEvilSkeleton]

I'll ask the Flathub maintainers if they approve this.

[TheEvilSkeleton]

I'm marking it as draft, since there is some consideration to deprecate the beta branch: #424. @mirkobrombin do you still want to deprecate or do we accept this MR? I'd prefer deprecating it to reduce workload for Flathub, and we already build flatpaks upstream.

[Kinsteen]

If you choose to deprecate the beta branch, I think it would be great to explain in the documentation how to install packages created by the CI in the original repo, so we can redirect people who have a breaking bug that has been fixed upstream to the docs