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_recipes.py

@@ -1,5 +1,5 @@
 from random import randint
-from typing import Any
+from typing import Any, Optional
 from uuid import UUID
 
 from sqlalchemy import and_, func
@@ -143,3 +143,13 @@ class RepositoryRecipes(RepositoryGeneric[Recipe, RecipeModel]):
             .order_by(func.random())  # Postgres and SQLite specific
             .limit(limit)
         ]
+
+    def get_by_slug(self, group_id: UUID, slug: str, limit=1) -> Optional[Recipe]:
+        dbrecipe = (
+            self.session.query(RecipeModel)
+            .filter(RecipeModel.group_id == group_id, RecipeModel.slug == slug)
+            .one_or_none()
+        )
+        if dbrecipe is None:
+            return None
+        return self.schema.from_orm(dbrecipe)