Traffic (access) policy should support https/tcp/...

[pilhuhn]

Currently the spec only mentions http. One may want to have different policies for http and https. E.g. block all http and only allow https to pass. Likewise for what Istio names 'tcp' - arbitrary protocols on top of tcp. And then later also differentiations by other (recognised) protocols. E.g. allow AMQP-based messaging but block telnet.