Set branding colors in AppStream metadata
Reason for the change
- Without these, Elisa can't be featured on FlatHub
- Soon Discover will show these colors on the app page and on app list/grid items
Test plan
N/A since support in Discover doesn't exist yet and getting it to use local dev session appstream data
Screenshots or screen recordings
Final appearance in Discover or on FlatHub TBH; but it should end up looking something like this:
Bugs fixed
N/A