Set the appropriate h2c appProtocol label so our K8s Services work with Gateway API

[dprotaso]

Feature Request

Currently we are not setting known appProtocol values to indicate our backends expect a certain protocol. This is the mechanic used by Gateway API implementations

ref: istio/istio#47610
ref: projectcontour/contour#5897

I think we should start with h2c first since we have a mechanic defined in our runtime contract to specify that protocol.

For websocket - this in theory should just be on by default (contour toggled it on for Gateway API). There might be other implementations that have this off but let's revisit that when we find one that doesn't

[gabo1208]

/assign

[dprotaso]

Interestingly enough I wonder if adding the app protocol broke net-gateway-api

see the dependency bump here: #14789

[dprotaso]

Verified with the networking conformance that this should work now with our net-gateway-api integration

knative-extensions/net-gateway-api#635