A version of #3203 where I keep it simple instead.

- Serve console at `/login/{silo_name}/local` without auth check
- Do not get rid of spoof login yet. People are using it on dogfood and
we don't have a great way to replace that
- Add `/v1` prefix to `POST /login/{silo_name}/local` and `POST /logout`
  - A few more endpoints are missing it but I'll get those later
- Change `POST /login/{silo_name}/local` success response from a 303
redirect to a 204
- This is definitely debatable, but because it's a JSON API endpoint,
it's hard for me to see why anyone would be in a situation where they
want to follow that redirect. The problem is that because it's made in
the background, the browser doesn't navigate to the redirect URL, the
background fetch just follows it and downloads the HTML. The TS client
errors out because it doesn't know what to do with HTML.
  - Alternatives:
- Use `redirect: manual` in `fetch()` call to prevent it following the
redirect. This does seem to work, but based on the
[spec](https://fetch.spec.whatwg.org/#concept-request-redirect-mode) it
really seems like you're not supposed to do this. The resulting response
is called an [opaque-filtered redirect
response](https://fetch.spec.whatwg.org/#concept-filtered-response-opaque-redirect)
and is not supposed to be good for anything but following the same
redirect _later_
- Fix `oxide.ts` to not error out on HTML. That would be
[here](https://github.com/oxidecomputer/oxide.ts/blob/8a376956b03422ade24471207ceb0ab8c8961c4e/client/http-client.ts#L103-L104).
It's feasible but it would complicate things and it doesn't seem
worthwhile.