Support optional CloudSQL proxy sidecar

[brtkwr]

Describe the feature request

I want unleash to optionally support cloudsql proxy sidecar as an alternative to postgres.

Background

At the moment we are using externally deployed cloudsql proxy hooked up to unleash but sometime, transient network issues prevent DNS resolution between unleash pod and gcloudsql proxy service, having it run as a sidecar is more secure and the recommended way of deploying cloudsql proxy which also prevents the service from being advertised in the namespace.

Solution suggestions

No response