Enhance `tcp` binding to route by `port`

[jfallows]

Is your feature request related to a problem? Please describe.
Multiple tcp server bindings in zilla.yaml for the same example is confusing, see zilla-examples.

Describe the solution you'd like
Support for tcp binding to route by port number, so that a single tcp server can route by port 8080 to http and by port 9090 to tls for https for example.

Describe alternatives you've considered
The current approach of multiple tcp server bindings, one per distinct port, works but is confusing.

Additional context
This will simplify the visualization in Zilla VS Code Extension.

[lukefallows]

I would like to take a go at this issue.