Expr: fix failure to execute due to OrgID (#29653)

* Expr: fix failure to execute due to OrgID
Get orgID from the plugin context, which makes more sense anyways.
makes expressions work again after https://github.com/grafana/grafana/pull/29449 changes.

* Do not save organisation on its alert query model

Co-authored-by: Sofia Papagiannaki <sofia@grafana.com>

pkg/expr/transform.go

@@ -73,7 +73,7 @@ func TransformData(ctx context.Context, req *backend.QueryDataRequest) (*backend
 	svc := Service{}
 	// Build the pipeline from the request, checking for ordering issues (e.g. loops)
 	// and parsing graph nodes from the queries.
-	pipeline, err := svc.BuildPipeline(req.Queries)
+	pipeline, err := svc.BuildPipeline(req)
 	if err != nil {
 		return nil, status.Error(codes.InvalidArgument, err.Error())
 	}