Implements Service Internal Traffic Policy

1. Add API definitions;
2. Add feature gate and drops the field when feature gate is not on;
3. Set default values for the field;
4. Add API Validation
5. add kube-proxy iptables and ipvs implementations
6. add tests

pkg/apis/core/zz_generated.deepcopy.go

@@ -5335,6 +5335,11 @@ func (in *ServiceSpec) DeepCopyInto(out *ServiceSpec) {
 		*out = new(string)
 		**out = **in
 	}
+	if in.InternalTrafficPolicy != nil {
+		in, out := &in.InternalTrafficPolicy, &out.InternalTrafficPolicy
+		*out = new(ServiceInternalTrafficPolicyType)
+		**out = **in
+	}
 	return
 }