Get collection usage size with ARM metrics call (#327)

- Removed `readCollectionQuotaInfo` call. The only data we need is the usage size which we can get via the ARM metrics call instead.
- Added `getCollectionUsageSize` which fetches the `DataUsage` and `IndexUsage` metrics, converts them to KB, and returns the sum as the total usage size

src/Explorer/Tree/ResourceTreeAdapter.test.tsx

@@ -229,9 +229,7 @@ const createMockCollection = (): ViewModels.Collection => {
   const mockCollectionVM: ViewModels.Collection = new Collection(
     createMockContainer(),
     "fakeDatabaseId",
-    mockCollection,
-    undefined,
-    undefined
+    mockCollection
   );
 
   return mockCollectionVM;