[Feature request]: flatpak * --installation={PATH}

[ryanabx]

Checklist

• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the issue tracker for a feature request that matches the one I want to file, without success.

Suggestion

I'd like manipulate flatpaks in a repo that is not defined in /etc/flatpak/installations.d/. Unsure if this is out of flatpak's scope or not, but I do think that it'd be nice to be able to reference flatpak repos via path instead of a named identifier from installations.d