feat: Use psycopg2 for Connection Pooling and Implement Global Engine with Context Manager for Session Management

[qcdyx]

Summary:

Closes #826

• Updated the database connection setup to use psycopg2 for connection pooling.
• Refactored the code to use a global SQLAlchemy engine.
• Implemented a context manager for managing database sessions.
• Ensured session isolation for each request to maintain data integrity and prevent conflicts.

Expected behavior:

• database connections are reused, reducing the overhead of creating new connections and improving performance.
• the context manager ensures that sessions are properly opened, committed, rolled back, and closed, providing robust transaction management.
• ensured that each request gets its own isolated session.

Load test shows that ramping to 5000 users at a rate of 50.00 per second uses 22 active connections - we have max 100 connections.

I'll work on a knowledge share sub-issue and explain all the changes in details.

Testing tips:

Provide tips, procedures and sample files on how to test the feature.
Testers are invited to follow the tips AND to try anything they deem relevant outside the bounds of the testing tips.

Please make sure these boxes are checked before submitting your pull request - thanks!

• Run the unit tests with ./scripts/api-tests.sh to make sure you didn't break anything
• Add or update any needed documentation to the repo
• Format the title like "feat: [new feature short description]". Title must follow the Conventional Commit Specification(https://www.conventionalcommits.org/en/v1.0.0/).
• Linked all relevant issues
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[davidgamez]

Amazing improvement!