CloudWatch/Logs: Fix log alerts in new unified alerting (#36558)

* Pass FromAlert header from new alerting

* Add better error messages

pkg/expr/graph.go

@@ -157,7 +157,7 @@ func (s *Service) buildGraph(req *Request) (*simple.DirectedGraph, error) {
 		case dsName == DatasourceName || dsUID == DatasourceUID:
 			node, err = buildCMDNode(dp, rn)
 		default: // If it's not an expression query, it's a data source query.
-			node, err = s.buildDSNode(dp, rn, req.OrgId)
+			node, err = s.buildDSNode(dp, rn, req)
 		}
 		if err != nil {
 			return nil, err

pkg/expr/nodes.go

@@ -142,6 +142,7 @@ type DSNode struct {
 	timeRange  TimeRange
 	intervalMS int64
 	maxDP      int64
+	request    Request
 }
 
 // NodeType returns the data pipeline node type.
@@ -149,7 +150,7 @@ func (dn *DSNode) NodeType() NodeType {
 	return TypeDatasourceNode
 }
 
-func (s *Service) buildDSNode(dp *simple.DirectedGraph, rn *rawNode, orgID int64) (*DSNode, error) {
+func (s *Service) buildDSNode(dp *simple.DirectedGraph, rn *rawNode, req *Request) (*DSNode, error) {
 	encodedQuery, err := json.Marshal(rn.Query)
 	if err != nil {
 		return nil, err
@@ -160,12 +161,13 @@ func (s *Service) buildDSNode(dp *simple.DirectedGraph, rn *rawNode, orgID int64
 			id:    dp.NewNode().ID(),
 			refID: rn.RefID,
 		},
-		orgID:      orgID,
+		orgID:      req.OrgId,
 		query:      json.RawMessage(encodedQuery),
 		queryType:  rn.QueryType,
 		intervalMS: defaultIntervalMS,
 		maxDP:      defaultMaxDP,
 		timeRange:  rn.TimeRange,
+		request:    *req,
 	}
 
 	rawDsID, ok := rn.Query["datasourceId"]
@@ -231,6 +233,7 @@ func (dn *DSNode) Execute(ctx context.Context, vars mathexp.Vars, s *Service) (m
 	resp, err := s.queryData(ctx, &backend.QueryDataRequest{
 		PluginContext: pc,
 		Queries:       q,
+		Headers:       dn.request.Headers,
 	})
 
 	if err != nil {

pkg/expr/transform.go

@@ -206,6 +206,7 @@ func (s *Service) queryData(ctx context.Context, req *backend.QueryDataRequest)
 	tQ := plugins.DataQuery{
 		TimeRange: &timeRange,
 		Queries:   queries,
+		Headers:   req.Headers,
 	}
 
 	// Execute the converted queries