CLI not generating correct examples for gRPC

[nitinmohan87]

If an attribute has nested type (e.g. MapOf(String, ArrayOf(String)) CLI should print out the correct examples to pass in the params

CLI should also print any unmarshal errors for easier debugging

[smessier]

there also seems to be a problem for CLI parsing MapOf(String, ArrayOf(String)) passed in a message argument. for example:

my_service-cli --url "localhost:8080" my action --message '{"headers": {"Foo": ["bar"]}}'
invalid JSON for message, example of valid JSON:
'{
  "headers": {
	 "key": [
		"value"
	 ]
  },
}'
run 'my_service-cli --help' for detailed usage.

stepping through the cli code in the debugger, the JSON parser is trying to unmarshal headers as map[string]*ArrayOfString where ArrayOfString is defined in the my.pb.go file as:

type ArrayOfString struct {
	state         protoimpl.MessageState
	sizeCache     protoimpl.SizeCache
	unknownFields protoimpl.UnknownFields

	Field []string `protobuf:"bytes,1,rep,name=field,proto3" json:"field,omitempty"`
}

this is odd because it seems protobuf should not be involved in the initial unmarshaling of the JSON message passed to CLI.