Chore: Rudderstack upgrade to SDK v3 behind flag (#114126)

* add rudderstack version upgrade feature flag

* add new rudderstack backend file
gate new backend with feature flag

* fix global type error

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

@@ -1188,4 +1188,9 @@ export interface FeatureToggles {
   * Enable TTL plugin instance manager
   */
   ttlPluginInstanceManager?: boolean;
+  /**
+  * Enables the new version of rudderstack
+  * @default false
+  */
+  rudderstackUpgrade?: boolean;
 }