## Problem
On Azure we need to use username-password authentication in proxy for
regional redis client.
## Summary of changes
This adds `redis_auth_type` to the config with default value of "irsa".
Not specifying it will enforce the `regional_redis_client` to be
configured with IRSA redis (as it's done now).
If "plain" is specified, then the regional client is condifigured with
`redis_notifications`, consuming username:password auth from URI. We
plan to do that for the Azure cloud.
Configuring `regional_redis_client` is required now, there is no opt-out
from configuring it.
https://github.com/neondatabase/cloud/issues/14462
7996bce6d6