Merge drf_spectacular OpenAPI docs and django-nijia OpenAPI docs

[JoshYuJump]

Now the docs has 2 urls.

# drf_spectacular OpenAPI docs
http://127.0.0.1:8000/api/docs/

# django-nijia OpenAPI docs
http://127.0.0.1:8000/api/agiles/docs/

Expect to merged into http://127.0.0.1:8000/api/docs/

[JoshYuJump]

We need Pydantic, but we don't need FastAPI. So django-nijia will be removed in next feature version.