feature: specify "main" ui in metadata/manifest #830
Description
Is your feature request related to a problem? Please describe.
Sometimes apps serve multiple UIs. We want to be able to know which to serve when opening via, e.g., App Store Launch button.
Describe the solution you'd like
App dev can optionally specify in manifest or metadata which is the "main" ui for a package/app
After this is implemented, this opens the door for @0x70b1a5 to add main-ui-respect to the App Store ui