refactor: add ConnectionName to ConnectionInfo class

[jackwotherspoon]

Adding ConnectionName to ConnectionInfo class to more closely match Go implementation.

Benefits:

• Cleaner interface, passing connection name around instead of individual args (project, region, instance)
• Consistent debug logs (give access to ConnectionName throughout)
• Allows us to tell if ConnectionInfo is using DNS (if ConnectionName.domain_name is set)

This will unblock DNS polling as we must know at the ConnectionInfo level if it is
configured via DNS domain name or not.

Related to #1169

[jackwotherspoon]

Lint will pass once we merge #1211 first