Configurable redis-instance name

[bkosciarz]

Summary

Currently the redis instance needs to be called redis-instance. Allow users to customize this and default to redis-instance if not provided.

Adds a fix to the cloud_sdk install which appears to be broken on Ubuntu20.04 (http -> https)

Testing

I only tested the prod deploy workflow and not staging, but it should be equivalent. I didn't touch _deploy_k8s which calls _get_redis_ip, but this should default to the default redis-instance case

[bkosciarz]

Can I get a /gcbrun?

This is ready for review

[bkosciarz]

@jonathanmetzman bumping this