Rename hostname to domain

In the bigbang values.yaml the first yaml key-pair is
hostname: bigbang.dev
This key is incorrectly named. This is a DOMAIN not a hostname. The key name should be
domain:
This incorrect name cascades down into all the Package repos as well. But this issue is scoped only for BigBang repo.

Changing the name of this key will be a breaking change for customers who have a saved values override yaml. But easy to adjust.

Questions for discussion:

1. Do we do this change slowly? In other words, we deprecate hostnames: but still support it for a release or two if it exists through conditional helm templating. We would put deprecation notices in the release notes indicating when it will be removed.
2. Do we do it quick and get it over with? Change it now, at the beginning of the next sprint, and put a breaking change upgrade notice in the release notes.
3. Do we name the new yaml key domain: or something else like domainName?