This change moves persistence for background, packages, and users to the persistence factory.
Changing `zcl_abapgit_persistence_user=>get_instance( )` to `zcl_abapgit_persist_factory=>get_user( )` will be a separate PR.
the old get_instance() method in ZCL_ABAPGIT_PERSIST_SETTINGS has been moved to a method in zcl_abapgit_persist_factory, plus interface added. Added to persist injector