feat(backup): hooks

selfprivacy_api/backup/__init__.py

@@ -37,4 +37,7 @@ class Backups(metaclass=SingletonMetaclass):
     def back_up(self, service: Service):
         folder = service.get_location()
         repo_name = service.get_id()
+
+        service.pre_backup()
         self.provider.backuper.start_backup(folder, repo_name)
+        service.post_restore()

selfprivacy_api/services/service.py

@@ -138,3 +138,9 @@ class Service(ABC):
     @abstractmethod
     def move_to_volume(self, volume: BlockDevice) -> Job:
         pass
+
+    def pre_backup(self):
+        pass
+
+    def post_restore(self):
+        pass