Fix network URL logging in `start-server` (#55260)
### What?
Follow-up of #54926.
While that PR's main fix is no longer necessary due to the removal of render workers, I figure that some changes are nice-to-have and have isolated them into this PR. This includes fixing `appUrl` and `networkUrl` in `start-server`, fixing docs and removing some unnecessary template literals in `turbopack-warning`.
### How?
`appUrl` now tries to use `hostname` instead of `actualHostname` (an address like `example.com` seems to be more useful here than an IP like `xxx.xxx.xxx.xxx`), and `networkUrl` is now prefixed with `http://`.
Other simple changes include fixing docs.
Co-authored-by: Zack Tanner <1939140+ztanner@users.noreply.github.com>
