Add MediaSession flag config file and new flags

The config file didn't exist yet for new MediaSession related
changes.

Add 3 new flags to the file to address some pending issues.

Test: n/a
Flag: com.android.media.mediasession.flags.add_wiu_allowlisting_to_media_button_receiver_holder_send
Flag: com.android.media.mediasession.flags.avoid_media_browser_include_capabilities_if_not_needed
Flag: com.android.media.mediasession.flags.remove_wiu_allowlisting_from_mediacontroller_sendcommand
Bug: 385736540
Bug: 393582077
Bug: 339637822
Change-Id: I16d4d29b36ad11c0bc4a30359b2d1bd5387906b8