Change the path though http header

[jinleileiking]

normal proto:

41 service Greeter {¬
  42   // Sends a greeting¬
  43   rpc SayHello (HelloRequest) returns (HelloReply) {¬
  44     option (google.api.http) = {¬
  46     post: "/Action/2017-01-01"¬
  47     body: "*"¬
  48   };¬
  49 }¬

For me, I need change the post: "/Action/2017-01-01" to post: "/{{Action}}/{{Version}}"

which Action and Version is http header.

[achew22]

I think this sort of change would require a change in the http<=>proto spec. Please feel free to open an issue in that repo and CC me.