airframe-rpc: Error handling with RPCException

[xerial]

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Add a standard method for handling exception in Airframe RPC.

Server side

• Throw an RPCException in RPC implementations using RPCStatus code #1973
• airframe-http needs to send RPCException to clients
  • finagle: embed RPCException to the HTTP response body #2141
  • gRPC: embed RPCException to the trailer #2139

Client side

• sbt-airframe should add a wrapper to convert the server side exception to RPCException #2166
• Introduce RPCHttpClient interface in order to consolidate error handling #2165
• http client side logging to record RPCException, which will be automatically retried #2142 #1820
• Read RPCException message from gRPC trailer