Add h2 gRPC Identifier

[matt-turner-skyscanner]

Issue Type:

• Bug report
• Feature request

Part IX of the k8s service mesh blog gives a good into to routing gRPC through l5d, but in a lot of ways it feels a bit 2nd class. One of our big issues is the need to use domainToPathPfx to extract the service name from the h2 path (supposing that format will never change), and even then that ignores the package so services have to be globally unique across k8s namespaces (we used a custom re-writer to work round that). It would be great to have a first-class gRPC identifier which pulled the service name (and perhaps the last section of the package name) from the packet (which happens to be an h2 header frame).

[wmorgan]

Thanks for filing this, @matt-turner-skyscanner!