Add usage tracking for SyncSubmodules

Author: jcansdale

src/GitHub.App/ViewModels/GitHubPane/PullRequestDetailViewModel.cs

@@ -657,9 +657,7 @@ IObservable<Unit> DoPush(object unused)
 
         IObservable<Unit> DoSyncSubmodules(object unused)
         {
-            return pullRequestsService.SyncSubmodules(LocalRepository);
-            // TODO: UsageTracker
-            // .Do(_ => usageTracker.IncrementPullRequestPushCount(IsFromFork).Forget());
+            return pullRequestsService.SyncSubmodules(LocalRepository).Do(_ => usageTracker.IncrementCounter(x => x.NumberOfSyncSubmodules).Forget());
         }
 
         class CheckoutCommandState : IPullRequestCheckoutState

src/GitHub.Exports/Models/UsageModel.cs

@@ -28,6 +28,7 @@ public class UsageModel
         public int NumberOfForkPullRequestsCheckedOut { get; set; }
         public int NumberOfForkPullRequestPulls { get; set; }
         public int NumberOfForkPullRequestPushes { get; set; }
+        public int NumberOfSyncSubmodules { get; set; }
         public int NumberOfWelcomeDocsClicks { get; set; }
         public int NumberOfWelcomeTrainingClicks { get; set; }
         public int NumberOfGitHubPaneHelpClicks { get; set; }