RAG application leaks DB connection objects

[bhlim]

With IAP enabled for the RAG application, the rag-frontend workload runs out of memory after a couple of days and stops serving. I traced this to a memory leak when serving http requests. With IAP, the K8s ingress server pings the http server continuously and exposes the leak more rapidly.

The culprit is at this line in frontend/container/cloud_sql.py.

This can be fixed by moving connector = Connector() into the if statement:

global db
if db is None:
connector = Connector()
db = init_connection_pool(connector)

[german-grandas]

Refactor made to the cloud_sql module on #648