This one is huge, and I'm sorry.
The problem is that once I change `tailnet.Conn` to start doing v2 behavior, I kind of have to change it everywhere, including in CoderSDK (CLI), the agent, wsproxy, and ServerTailnet.
There is still a bit more cleanup to do, and I need to add code so that when we lose connection to the Coordinator, we mark all peers as LOST, but that will be in a separate PR since this is big enough!
re: #10528
Refactors PG Coordinator to work with the Tailnet v2 API, including wrappers for the existing v1 API.
The debug endpoint functions, but doesn't return sensible data, that will be in another stacked PR.
