async support

[Matvii-Boichenko]

It would be nice to have instruction how to use SQLAlchemy async session with asyncpg with Flask-SQLAlchemy. I saw an issue opened in 2022 with similar request. It was closed because there were no need to rewrite library with async approach, however it was said that SQLAlchemy async session is already possible to implement with current library version overriding several methods. So, it would be very useful to get instruction on what exactly implementation is suggested.

[nioncode]

Did you find out how to override the engine to return an async engine? I only found how to override the arguments that are passed to create_engine, but we need to call create_async_engine.