SQLAlchemy 2.0

[Net-Mist]

Hello,

This PR make this code compatible with SQLAlchemy 2 and all unit-tests should be passing (they are on my fork).
I started from #256.

• fixes Migrate to SQLAlchemy 2.0 #259 Support for Sqlalchemy 2.0? #242

Checklist:

• Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• Add or update relevant docs, in the docs folder and in code.
• Ensure PR doesn't contain untouched code reformatting: spaces, etc.
• Run flake8 and fix issues.
• Run pytest no tests failed. See https://clickhouse-sqlalchemy.readthedocs.io/en/latest/development.html.

[coveralls]

coverage: 85.756% (-0.2%) from 85.952% when pulling 9a14437 on Net-Mist:sa-2.0 into e16d482 on xzkostyan:master.

[xzkostyan]

Thanks.

I'll make 0.3.0 release on next week.

[xzkostyan]

Version 0.3.0 with SQLAlchemy 2.0 released.