Migrate the api to use FastAPI instead

[xbarra]

We have been discussing in the meeting the migration of the code in physrisk api so that it uses fastapi instead of flask.

@NickKellett has been working on this

[NickKellett]

I got stuck, but luckily this will be addressed by Joe's PR #64

[joemoorhouse]

Oops, should have used this issue!