server lifecycle docs are sparse, wrong

In the latest release, the docs for HttpServerStarter say:

You must invoke start() on the returned instance of HttpServerStarter (and await the result) to actually start the server.

I'm not sure if that was true in 0.6.0, but I don't think it's true today. start() appears to spawn one or more tasks that run the server. (I'm not sure if this is the task spawned by the wrapped start() methods or one started by hyper, but empirically, it does appear to be true.) You don't have to await on the server itself unless you want to wait for the server to stop.

That comment is still in "main":
https://github.com/oxidecomputer/dropshot/blob/main/dropshot/src/server.rs#L229-L236

But that's now on a private function on a private type. In "main", the public HttpServerStarter::new and HttpServerStarter::start have no docs:
https://github.com/oxidecomputer/dropshot/blob/main/dropshot/src/server.rs#L98
https://github.com/oxidecomputer/dropshot/blob/main/dropshot/src/server.rs#L154

Even in the released version, this whole process seems underdocumented.

Read dropshot/src/server.rs at the public HttpServerStarter::new and start methods (around lines 98 and 154), then compare them with the stale private documentation around lines 229-236. Clarify the lifecycle, including when start() runs the server and what awaiting the server does, and document the complete process for users.