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/Controls/Settings/SettingsSubComponents/ScaleComponent.tsx

@@ -186,7 +186,7 @@ export class ScaleComponent extends React.Component<ScaleComponentProps> {
       onScaleSaveableChange={this.props.onScaleSaveableChange}
       onScaleDiscardableChange={this.props.onScaleDiscardableChange}
       getThroughputWarningMessage={this.getThroughputWarningMessage}
-      usageSizeInKB={this.props.collection.quotaInfo().usageSizeInKB}
+      usageSizeInKB={this.props.collection.usageSizeInKB()}
     />
   );
 

src/Explorer/Controls/Settings/SettingsSubComponents/__snapshots__/ScaleComponent.test.tsx.snap

@@ -58,6 +58,7 @@ exports[`ScaleComponent renders with correct initial notification 1`] = `
       spendAckChecked={false}
       throughput={1000}
       throughputBaseline={1000}
+      usageSizeInKB={100}
       wasAutopilotOriginallySet={true}
     />
     <Stack

src/Explorer/Controls/Settings/TestUtils.tsx

@@ -18,7 +18,7 @@ export const collection = ({
     excludedPaths: []
   }),
   uniqueKeyPolicy: {} as DataModels.UniqueKeyPolicy,
-  quotaInfo: ko.observable<DataModels.CollectionQuotaInfo>({} as DataModels.CollectionQuotaInfo),
+  usageSizeInKB: ko.observable(100),
   offer: ko.observable<DataModels.Offer>({
     autoscaleMaxThroughput: undefined,
     manualThroughput: 10000,

src/Explorer/Controls/Settings/__snapshots__/SettingsComponent.test.tsx.snap

@@ -1300,9 +1300,9 @@ exports[`SettingsComponent renders 1`] = `
                 "version": 2,
               },
               "partitionKeyProperty": "partitionKey",
-              "quotaInfo": [Function],
               "readSettings": [Function],
               "uniqueKeyPolicy": Object {},
+              "usageSizeInKB": [Function],
             }
           }
           container={
@@ -3871,9 +3871,9 @@ exports[`SettingsComponent renders 1`] = `
                 "version": 2,
               },
               "partitionKeyProperty": "partitionKey",
-              "quotaInfo": [Function],
               "readSettings": [Function],
               "uniqueKeyPolicy": Object {},
+              "usageSizeInKB": [Function],
             }
           }
           container={