DashboardGrid: Add support to filter panels using variable (#77112)

* DashboardGrid panel filter

* Missed segment and changes per PR discussion

* Hide feature flag from docs

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Co-authored-by: Dominik Prokop <dominik.prokop@grafana.com>

packages/grafana-data/src/types/featureToggles.gen.ts

@@ -157,4 +157,5 @@ export interface FeatureToggles {
   annotationPermissionUpdate?: boolean;
   extractFieldsNameDeduplication?: boolean;
   dashboardSceneForViewers?: boolean;
+  panelFilterVariable?: boolean;
 }