Introduce remove_app_profiler_pss_collection flag

This change adds a flag config for android.os for replacing background
PSS collection in AppProfiler with RSS.

This flag config is added to the android.os package instead of
com.android.server.am because the feature will rely on a new Debug API.
Having the flag here allows it to be used for both @FlaggedApi in
android.os.Debug as well as for a runtime check in AppProfiler.

Test: Use a test change to check that the flag can be set and read from
      AppProfiler.
Bug: 297542292
Bug: 296454553
Change-Id: I7e145d9eea8bf47999cb533efd921c4fdc3baace