[Feature Request] Support AWS RDS IAM Authentication

[shadow625]

Description

Currently, the rag_api connects to the database using standard username/password authentication as seen in database.py line 11
Our team are doing some enhancement on the RDS include adopting AWS IAM Authentication, which will use short-lived authentication tokens instead of storing database passwords. So we want to ask here to support AWS IAM Authentication.

Proposed Solution

Implement AWS IAM authentication support for RDS connections.

Reference:

asyncpg
IAM Authentication for RDS
Using IAM Authentication with PostgreSQL