code: func WithFieldExtractorForInitialReq(f RequestFieldExtractorFunc) Option {
  	return func(o *options) {
  		o.requestFieldsFunc = f
  		o.requestFieldsFromInitial = true
  	}
  }
docs: // WithFieldExtractorForInitialReq customizes the function for extracting log fields from protobuf messages,
  // for all unary and streaming methods. For client-streams and bidirectional-streams, the tags will be
  // extracted from the first message from the client.