Add example for mongodb

[jet10000]

I found example for sqlalchemy(SQL), Please add a example for odmantic(mongodb)

https://art049.github.io/odmantic/usage_fastapi/

[IndominusByte]

The purpose of this extension for authorization, not authentication so you can use it without a database, you can see later in documentation (under development). if you have any question please don't be hesitate 🙏