Correlations: Hide Correlations Page behind a feature toggle (#55224)

* Hide Correlations Page behind a toggle

* Remove redundant defaults

* Ensure top nav is rendered when correlations are disabled

This is for the case when:

[feature_toggles]
topnav = true

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

@@ -46,6 +46,7 @@ export interface FeatureToggles {
   exploreMixedDatasource?: boolean;
   tracing?: boolean;
   commandPalette?: boolean;
+  correlations?: boolean;
   cloudWatchDynamicLabels?: boolean;
   datasourceQueryMultiStatus?: boolean;
   traceToMetrics?: boolean;