Enforce lowercase service names

[pglass]

Changes proposed in this PR:

With the auth method, the service token relies on a service identity, which requires a lowercase name. This updates the binary to:

• Validate service names are lowercase in the schema.json. Actually, require they match the service identity regex. I also handled this for the gateway service name and update schema validation for this.
• When no service name is specified, fall back to the lowercase family name.

How I've tested this PR:

Unit and acceptance tests

How I expect reviewers to test this PR:

👀

Checklist:

• Tests added
• CHANGELOG entry added

[pglass]

This is empty string (^$) or the service identity regex from Consul.

[cthain]

Question: I'm not clear on why null is defined as a valid type when the fields themselves aren't required. Is this to allow for the possibility to define the config like "lanAddress": null?

[pglass]

Yeah, it's kind of silly, but I setup the config schema this way because it slightly simplifies passing fields from the Terraform module. We don't have to worry in Terraform whether a field is null or a value (string, list, int, etc) for it to pass validation, since there are so many fields we don't specify by default.

It may not make as much sense for some of these fields. And we've stopped using null so much for default values in the Terraform module, so maybe we could rethink this.