add Healthy model

src/fastapi_app/lib/api/v1/schemas/entity.py

@@ -6,3 +6,7 @@ import pydantic
 class Token(pydantic.BaseModel):
     sub: uuid.UUID
     exp: int | None = None
+
+
+class Healthy(pydantic.BaseModel):
+    status: str = pydantic.Field(..., example="healthy", description="Схема доступности сервиса")