Add option to run flatpak-builder-lint after build

[vchernin]

This action could run similar checks as to what flathub builders do, e.g. via a new action input lint: boolean. There already exists an action in the obs repo which works but is yet more scripts to add in CI.

https://github.com/obsproject/obs-studio/blob/e1e1b6daabf838a36e14436e1efdd4f38533a00d/.github/actions/flatpak-builder-lint/action.yaml
https://github.com/obsproject/obs-studio/blob/e1e1b6daabf838a36e14436e1efdd4f38533a00d/.github/workflows/build-project.yaml#L303-L326

Since this repo's action already knows where the build directory is, the lints for builddir,repo,manifest,appstream could be more easily run as part of this action.

The lint checks are all fast enough so it is probably reasonable to keep them under one option.

[Boria138]

I have a similar error when checking absolutely any metainfo file

The problem tag could not be redefined: The severity of the "cid-domain-not-lowercase" tag cannot be lowered to a level that allows it to pass verification.

So I don't think that's a good idea.

[bbhtt]

flatpak-builder-lint depends on patches of appstream available in org.flatpak.Builder, it cannot be used elsewhere https://github.com/flathub-infra/flatpak-builder-lint?tab=readme-ov-file#installation

The only supported ways to install and use it are Docker and Flatpak.