With the management tunnels work, we allow calls to our edge service
using an access JWT provided by Tunnelstore. Given a connector ID,
this request is then proxied to the appropriate Cloudflare Tunnel.
This PR takes advantage of this flow and adds a new host_details
endpoint. Calls to this endpoint will result in cloudflared gathering
some details about the host: hostname (os.hostname()) and ip address
(localAddr in a dial).
Note that the mini spec lists 4 alternatives and this picks alternative
3 because:
1. Ease of implementation: This is quick and non-intrusive to any of our
code path. We expect to change how connection tracking works and
regardless of the direction we take, it may be easy to keep, morph
or throw this away.
2. The cloudflared part of this round trip takes some time with a
hostname call and a dial. But note that this is off the critical path
and not an API that will be exercised often.
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