Added Deploy as Statefulset Option

[oliverisaac]

What this PR does / why we need it:

If one is deploying more than 5 DB proxies then an internal loadbalancer on google is not supported as they must have at most 5 ports.

To fix this, I added the option to deploy as statefulset which allows you to then access the proxy using the headless service's FQDN to get A records:

# In cluster:
dig cloudsql-proxy-headless.cloudsql-proxy.svc.cluster.local
# Returns multiple A records,  one for each replica

Special notes for your reviewer:

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• [ x ] Chart Version bumped
• [ x ] Changes are documented in the README.md

[rimusz]

Thanks for the PR 👍