[MM-35077] Add basic support for plugin intra-cluster communication (#17495)

* Add basic support for plugin intra-cluster communication

* Some renaming for added clarity

* Allow sending cluster event to specific nodes

* Improve naming and documentation

* Improve logging

einterfaces/cluster.go

@@ -21,7 +21,8 @@ type ClusterInterface interface {
 	HealthScore() int
 	GetMyClusterInfo() *model.ClusterInfo
 	GetClusterInfos() []*model.ClusterInfo
-	SendClusterMessage(cluster *model.ClusterMessage)
+	SendClusterMessage(msg *model.ClusterMessage)
+	SendClusterMessageToNode(nodeID string, msg *model.ClusterMessage) error
 	NotifyMsg(buf []byte)
 	GetClusterStats() ([]*model.ClusterStats, *model.AppError)
 	GetLogs(page, perPage int) ([]string, *model.AppError)

einterfaces/mocks/ClusterInterface.go

@@ -191,9 +191,23 @@ func (_m *ClusterInterface) RegisterClusterMessageHandler(event string, crm eint
 	_m.Called(event, crm)
 }
 
-// SendClusterMessage provides a mock function with given fields: cluster
-func (_m *ClusterInterface) SendClusterMessage(cluster *model.ClusterMessage) {
-	_m.Called(cluster)
+// SendClusterMessage provides a mock function with given fields: msg
+func (_m *ClusterInterface) SendClusterMessage(msg *model.ClusterMessage) {
+	_m.Called(msg)
+}
+
+// SendClusterMessageToNode provides a mock function with given fields: nodeID, msg
+func (_m *ClusterInterface) SendClusterMessageToNode(nodeID string, msg *model.ClusterMessage) error {
+	ret := _m.Called(nodeID, msg)
+
+	var r0 error
+	if rf, ok := ret.Get(0).(func(string, *model.ClusterMessage) error); ok {
+		r0 = rf(nodeID, msg)
+	} else {
+		r0 = ret.Error(0)
+	}
+
+	return r0
 }
 
 // StartInterNodeCommunication provides a mock function with given fields: