feat: creating FastAPI routes for working with cards

Added 3 routes:
- add_card (add a card via POST request with AddCardBody scheme)
- get_card (get a specific card by card_id)
- get_random_cards (get 10 random cards)

app/schemas/api_schemas.py

@@ -13,4 +13,10 @@ class AddUserBody(BaseModel):
 
     first_name: str
     last_name: str
-    photo_url: str
+    photo_url: str
+
+class AddCardBody(BaseModel):
+    choice_A: str
+    choice_B: str
+
+    author_id: NonNegativeInt