Add check-fastlane-as-fallback tool

Checks if upstream provides fastlane metadata at the latest specified commit. If yes then this tool remove description and summary from app metadata. Without args this will run on every metadata, file can passed as arg.

Often people add fastlane metadata but F-Droid doesn't pick fastlane cause our metadata "overwrites" fastlane.

Currently this affect 75 files. I will try to open MRs in parts. And after these are merged, I try to run this tool weekly or so and open a MR containing the results.

Ping @eighthave

Maybe is it not needed to add this in the the gitlab CI, and only add this tool to the repo, that we have such a tool everyone can use.