Added validators for users and recipes (#1052)

* Added validators for users and recipes

provide a simple get api, allowing to test for existence of
- user by username
- recipe by slug
- group by name (not tested yet)

* updated formatting

* Use group_id+slug for recipes, use ValidationRespone

* Fixed Flake8 errors and warnings

* add missing field for TestUser init

mealie/repos/repository_users.py

@@ -1,5 +1,6 @@
 import random
 import shutil
+from typing import Optional
 
 from mealie.assets import users as users_assets
 from mealie.schema.user.user import PrivateUser, User
@@ -34,3 +35,9 @@ class RepositoryUsers(RepositoryGeneric[PrivateUser, User]):
         # Delete the user's directory
         shutil.rmtree(PrivateUser.get_directory(id))
         return entry
+
+    def get_by_username(self, username: str, limit=1) -> Optional[User]:
+        dbuser = self.session.query(User).filter(User.username == username).one_or_none()
+        if dbuser is None:
+            return None
+        return self.schema.from_orm(dbuser)