aioauth-fastapi demo server and example

[aliev]

I created the demo server of aioauth on FastAPI. The project repository will live here: https://github.com/aliev/aioauth-fastapi

Demo server was deployed to heroku, so it can be easily tested with one of these playgrounds:

https://openidconnect.net/
https://oidcdebugger.com/

There are plans to add OpenID support, but I think there will be a few lines of code.

Simple authorization and registration was also added, access to the current user through request.user.

I also added FastAPI integration to aioauth core: https://github.com/aliev/aioauth/tree/master/aioauth/fastapi

I have a plan to add the models with CRUD operations of AuthorizationCode, Token and Code for turtoise, databases and sqlalchemy.

cc @woile @synchronizing