Add message queue agent (#6463)

* scaffold message queue agent

* adjust proto, add mq_agent

* add agent client implementation

* remove unused function

* agent publish server implementation

* adding agent

weed/mq/client/agent_client/agent_publish.go

@@ -0,0 +1,14 @@
+package agent_client
+
+import (
+	"github.com/seaweedfs/seaweedfs/weed/pb/mq_agent_pb"
+	"github.com/seaweedfs/seaweedfs/weed/pb/schema_pb"
+)
+
+func (a *PublishSession) PublishMessageRecord(key []byte, record *schema_pb.RecordValue) error {
+	return a.stream.Send(&mq_agent_pb.PublishRecordRequest{
+		SessionId: a.sessionId,
+		Key:       key,
+		Value:     record,
+	})
+}