Update metadata to pass appstreamtest

Summary:
KF6 has stricter rules for the app metadata. This commit makes enough changes so that there are no warnings or infos when verifying the app metadata.

Type: skip

CCBUG: https://iron.lily-is.land/T85

Test Plan: Verify that appstreamtest passes under both KF5/Qt5 and KF6/Qt6.

Reviewers: O1 the Kazv Project, nannanko

Reviewed By: O1 the Kazv Project, nannanko

Differential Revision: https://iron.lily-is.land/D46