Initial pass at PostgreSQL session management

[artificial-aidan]

Summary

• Add postgres_session.py
  • Implements session management using PostgreSQL
  • Accepts a pool as a default argument
  • Additional class method for creation from a connection string
• Add optional-dependency for psycopg

Test plan

Tests were written mocking the postgres calls. This was tested locally against a docker postgres database, with a variety of input messages.

Issue number

Related to #745

Checks

• I've added new tests (if relevant)
• I've added/updated the relevant documentation
• I've run make lint and make format
• I've made sure tests pass

[artificial-aidan]

Wanted to get the code up here in case there was some discussion on how to do things. Will look into the documentation tomorrow.

[artificial-aidan]

Got a little stuck on the old_version_test needed to have the pyscopg extras installed, not sure how litellm is working. I updated the make target to include all extras when testing python 3.9. Let me know if this isn't the path you'd prefer.

I took a stab at documentation. Open to feedback on structuring. Overall I wanted the postgres session to be in extensions because psycopg can be somewhat heavy on certain platforms. But I wasn't sure if the docs should go with extensions or the other memory docs.

[rm-openai]

@artificial-aidan lmk if this is ready for review and i can take a pass!

[artificial-aidan]

Should be ready now. Have been running it in our testing for about a week now.

[artificial-aidan]

Tests fixed. Missed the test changes I had made locally.