Add option to disable prepared statements.

[bosmobosmo]

The helm chart doesn't work out of the box when using PgBouncer in transaction pooling mode because it doesn't support prepared statements. An issue I've encountered is that the page would reload multiple times when trying to login, due to PG error in the background.
I've tested the solution suggested in here and this solves the login issue for me. Having a parameter to configure these values would be nice.