Add grpc plugin (#2758)

* Add grpc plugin

* remove stale readmes

client/grpc/message.go

@@ -0,0 +1,40 @@
+package grpc
+
+import (
+	"go-micro.dev/v5/client"
+)
+
+type grpcEvent struct {
+	topic       string
+	contentType string
+	payload     interface{}
+}
+
+func newGRPCEvent(topic string, payload interface{}, contentType string, opts ...client.MessageOption) client.Message {
+	var options client.MessageOptions
+	for _, o := range opts {
+		o(&options)
+	}
+
+	if len(options.ContentType) > 0 {
+		contentType = options.ContentType
+	}
+
+	return &grpcEvent{
+		payload:     payload,
+		topic:       topic,
+		contentType: contentType,
+	}
+}
+
+func (g *grpcEvent) ContentType() string {
+	return g.contentType
+}
+
+func (g *grpcEvent) Topic() string {
+	return g.topic
+}
+
+func (g *grpcEvent) Payload() interface{} {
+	return g.payload
+}