appstream-data: Add method of checking for appstream updates

[sheepman4267]

It would be extremely helpful to have a system in place to check when Appstream data needs to be regenerated before sync. I'd like this to take the form of a script living alongside the appstream-data package files, which could be run manually or triggered via CI depending on how much time it takes.

Off the top of my head, this could integrate output from worklog.py and cross-reference with the existing tooling to check if appstream data is needed (based on .desktop file being in the package). If we see a package change containing appstream data, then we need to update appstream data.

This meshes well with my existing (but not written down) idea to add a Taskfile to the appstream-data package which allows for easy package updates.