[am] Add logging for FGS type change

We don't event log when an already foreground service changes its FGS
type.

Add explicit warning logging, since this could result in difficult to
detect permission issues when capabilities change.

Test: atest CtsMediaAudioPermissionTestCases
Bug: 392905501
Flag: EXEMPT logging
Change-Id: I584159016f8df77d2f833892a94f96993e2c68c3