Fix schema creation errors while adding a new connection

[Anish9901]

Fixes #3420

Technical details

It seems like Brent already had this potential failure in mind while working on implementing Connection RPC endpoints and the error handling was appropriately added. The exception class added however was the base exception for the underlying SQLAlchemy exception that was being generated, as detailed in the issue. This PR aims to improve this behavior by catching the specific SQLAlchemy exception rather than its base. Additionally, we validate if the SQLAlchemy exception is raised by the anticipated base psycopg exception class. This is necessary because a SQLAlchemy exception inherits multiple psycopg exceptions within the same class hierarchy.

Video showcasing the new behavior

Screen.Recording.2024-03-15.at.1.46.43.PM.mp4

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• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no
  visible errors.

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[mathemancer]

Good catch.