Flipper Zero Application build utils

Typically for usage from build script.

It do following things: 1. Build FAP manifest using fam crate 2. Read env var FLIPPER_REPO_PATH 3. Copy or link (now just link) the output dir where manifest (fam) is to $FLIPPER_REPO_PATH/applications_user/{fap-id}/ 4. Same for assets such as icons

After this you can just execute ./fbt firmware_{fap-id} from the root flipperzero-firmware repository clone.

$FLIPPER_REPO_PATH should points to working copy of the flipperzero-firmware repository.

Example.