Support asyncpg with SQLAlchemy 1.4

[amotl]

Hi there,

within crate/crate-python#391, I am trying to add support for SQLAlchemy 1.4. By working on it and more specifically through [1,2], I learned that

SQLAlchemy version 1.4 and later supports the asyncpg dialect natively.

So, this might be an interesting option to consider.

With kind regards,
Andreas.

[1] https://docs.sqlalchemy.org/en/14/orm/extensions/asyncio.html
[2] MagicStack/asyncpg@3d0e23fe

P.S.: Also linking to MagicStack/asyncpg#6 and apache/superset#7018 here.

[amotl]

Appropriate SQLAlchemy support for Python's Stackless spin-off Greenlet also just got merged, see sqlalchemy/sqlalchemy#5615 and sqlalchemy/sqlalchemy#5616.

[amotl]

crate/crate-python#532 makes a stab at supporting this. It is experimental, and undecided about.