Add new Portal Backend Sample Data API and remove Notifications API references (#1965)

* Fixed Sample Data logic and remove notifications references

* fixed undefined

* fixed unit tests

* fixed format test

* cleanup

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Co-authored-by: Asier Isayas <aisayas@microsoft.com>

src/Explorer/Controls/Settings/SettingsUtils.test.tsx

@@ -44,7 +44,6 @@ describe("SettingsUtils", () => {
         readSettings: undefined,
         onSettingsClick: undefined,
         loadOffer: undefined,
-        getPendingThroughputSplitNotification: undefined,
       } as ViewModels.Database;
     };
     newCollection.offer(undefined);