Add RAG Agent to AutoGen Studio

[Knucklessg1]

Why are these changes needed?

RAG is one of the highest value agents. With support for Postgres and PGVector, it is highly desired to get RAG Agents incorporated into AutoGen Studio.

Related issue number

Closes #1723

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.