Allow the user to change the BackupTransport

Set the following config overlays to activate this feature:

* config_backup_settings_intent to settings://com.android.settings.backup.transport


* config_backup_settings_label to some user-facing label
  e.g. Change backup provider
* config_ignored_backup_transports to hide transports from the list

Co-authored-by: Michael Bestas <mkbestas@lineageos.org>
Change-Id: I080d96e2c34045a0e61f3fa1b839f463550f2028