[MM-13704] Updated CLI "deleter user" to also permanently delete GroupMembers associated to user (#12858)

* [MM-13704] Updated CLI to set DeleteAt in groupmemebrs

* [MM-13704] Updated Mock Test

* [MM-13704] Refactored to use current pattern to write function

* [MM-13704] Small text change

* [MM-13704] updated translation

* [MM-13704] Updated params of error function

* [MM-13704] Fixed confusion between channel and group store

* [MM-13704] Addressed PR comments

* [MM-13704] Added test case

* [MM-13704] Fixed err declaration

app/user.go

@@ -1456,6 +1456,10 @@ func (a *App) PermanentDeleteUser(user *model.User) *model.AppError {
 		return err
 	}
 
+	if err := a.Srv.Store.Group().PermanentDeleteMembersByUser(user.Id); err != nil {
+		return err
+	}
+
 	if err := a.Srv.Store.Post().PermanentDeleteByUser(user.Id); err != nil {
 		return err
 	}