cloudflared docker diag: include port in last step

### Existing documentation URL(s)

- https://developers.cloudflare.com/cloudflare-one/networks/connectors/cloudflare-tunnel/troubleshoot-tunnels/diag-logs/#docker

### What changes are you suggesting?

Unlike the "Host environment" section, the docker section does show how to override the port with the `--metrics` option.
In the first step it tells you to get it, use it for checking connectivity in step 3 but then step 4 doesn't tell you how to use it and assumes you use standard ports.

I propose an extra command like "If you are using a non-standard port for the metrics server, specify the ..." like in the Host env section.

### Additional information

_No response_