Document --service-uri on 'devtunnel create' for choosing the cluster

[joetossell]

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devtunnel create selects the cluster by nearest-by-latency, and there's no documented way
to override it. In practice --service-uri does exactly that, but it isn't listed in
devtunnel create --help or the CLI command reference, so it's undiscoverable:

# nearest cluster was euw at the time; this still created in uks1:
devtunnel create my-tunnel --service-uri https://uks1.rel.tunnels.api.visualstudio.com
devtunnel list | grep my-tunnel   # -> my-tunnel.uks1

The relay hostnames come from the URI column of devtunnel clusters.

Please surface --service-uri (or whatever the supported create-time cluster selector is)
in devtunnel create --help and the command-line reference. Choosing the cluster matters
because the tunnel's public URL encodes it, so anyone registering that URL with an external
service (webhook, OIDC redirect) needs it to be deterministic.

Environment

• devtunnel CLI 1.0.1824+9e602bae78, Linux x64, Microsoft Entra ID auth.

Related

• Behaviour side of the same root cause (default routing flaps / silently duplicates across
  clusters): filed separately as devtunnel create routing flaps between near-equidistant clusters, silently creating cross-cluster duplicates #642.