SSE: Support for ML query node (#69963)

* introduce a new node-type ML and implement a command outlier that uses ML plugin as a source of data.
* add feature flag mlExpressions that guards the feature

pkg/expr/graph.go

@@ -11,6 +11,7 @@ import (
 	"gonum.org/v1/gonum/graph/topo"
 
 	"github.com/grafana/grafana/pkg/expr/mathexp"
+	"github.com/grafana/grafana/pkg/services/featuremgmt"
 )
 
 // NodeType is the type of a DPNode. Currently either a expression command or datasource query.
@@ -21,6 +22,8 @@ const (
 	TypeCMDNode NodeType = iota
 	// TypeDatasourceNode is a NodeType for datasource queries.
 	TypeDatasourceNode
+	// TypeMLNode is a NodeType for Machine Learning queries.
+	TypeMLNode
 )
 
 func (nt NodeType) String() string {
@@ -29,6 +32,8 @@ func (nt NodeType) String() string {
 		return "Expression"
 	case TypeDatasourceNode:
 		return "Datasource"
+	case TypeMLNode:
+		return "Machine Learning"
 	default:
 		return "Unknown"
 	}
@@ -159,6 +164,7 @@ func (s *Service) buildGraph(req *Request) (*simple.DirectedGraph, error) {
 
 		rn := &rawNode{
 			Query:      rawQueryProp,
+			QueryRaw:   query.JSON,
 			RefID:      query.RefID,
 			TimeRange:  query.TimeRange,
 			QueryType:  query.QueryType,
@@ -171,7 +177,16 @@ func (s *Service) buildGraph(req *Request) (*simple.DirectedGraph, error) {
 			node, err = s.buildDSNode(dp, rn, req)
 		case TypeCMDNode:
 			node, err = buildCMDNode(dp, rn)
-		default:
+		case TypeMLNode:
+			if s.features.IsEnabled(featuremgmt.FlagMlExpressions) {
+				node, err = s.buildMLNode(dp, rn, req)
+				if err != nil {
+					err = fmt.Errorf("fail to parse expression with refID %v: %w", rn.RefID, err)
+				}
+			}
+		}
+
+		if node == nil && err == nil {
 			err = fmt.Errorf("unsupported node type '%s'", NodeTypeFromDatasourceUID(query.DataSource.UID))
 		}