feat: add --ssh-host-prefix flag for "coder ssh" (#16088)

This adds a flag matching `--ssh-host-prefix` from `coder config-ssh` to
`coder ssh`. By trimming a custom prefix from the argument, we can set
up wildcard-based `Host` entries in SSH config for the IDE plugins (and
eventually `coder config-ssh`).

We also replace `--` in the argument with `/`, so ownership can be
specified in wildcard-based SSH hosts like `<owner>--<workspace>`.

Replaces #16087.

Part of https://github.com/coder/coder/issues/14986.

Related to https://github.com/coder/coder/pull/16078 and
https://github.com/coder/coder/pull/16080.

cli/testdata/coder_ssh_--help.golden

@@ -45,6 +45,11 @@ OPTIONS:
   -R, --remote-forward string-array, $CODER_SSH_REMOTE_FORWARD
           Enable remote port forwarding (remote_port:local_address:local_port).
 
+      --ssh-host-prefix string, $CODER_SSH_SSH_HOST_PREFIX
+          Strip this prefix from the provided hostname to determine the
+          workspace name. This is useful when used as part of an OpenSSH proxy
+          command.
+
       --stdio bool, $CODER_SSH_STDIO
           Specifies whether to emit SSH output over stdin/stdout.