Import: fix dashboard imports with expressions (#43630) (#43680)

(cherry picked from commit b09d498484)

Co-authored-by: Ryan McKinley <ryantxu@gmail.com>

pkg/plugins/manager/dashboard_import.go

@@ -6,6 +6,7 @@ import (
 	"regexp"
 
 	"github.com/grafana/grafana/pkg/components/simplejson"
+	"github.com/grafana/grafana/pkg/expr"
 	"github.com/grafana/grafana/pkg/plugins"
 )
 
@@ -47,6 +48,13 @@ func (e *DashTemplateEvaluator) Eval() (*simplejson.Json, error) {
 		inputType := inputDefJson.Get("type").MustString()
 		input := e.findInput(inputName, inputType)
 
+		// force expressions value to `__expr__`
+		if inputDefJson.Get("pluginId").MustString() == expr.DatasourceType {
+			input = &plugins.ImportDashboardInput{
+				Value: expr.DatasourceType,
+			}
+		}
+
 		if input == nil {
 			return nil, &DashboardInputMissingError{VariableName: inputName}
 		}