Fix disk space issue in .NET PR creation by implementing sparse checkout

packages/http-client-csharp/eng/scripts/Submit-AzureSdkForNetPr.ps1

@@ -70,14 +70,48 @@ New-Item -ItemType Directory -Path $tempDir -Force | Out-Null
 Write-Host "Created temp directory: $tempDir"
 
 try {
-    # Clone the repository
-    Write-Host "Cloning azure-sdk-for-net repository..."
-    git clone "https://github.com/$RepoOwner/$RepoName.git" $tempDir
+    # Use sparse checkout to clone only the necessary files
+    # This significantly reduces disk space usage as azure-sdk-for-net is a very large repository
+    Write-Host "Setting up sparse checkout for azure-sdk-for-net repository..."
+
+    # Initialize empty git repository
+    git init $tempDir
     if ($LASTEXITCODE -ne 0) {
-        throw "Failed to clone repository"
+        throw "Failed to initialize repository"
     }
-
+    
     Push-Location $tempDir
+
+    # Add the remote
+    git remote add origin "https://github.com/$RepoOwner/$RepoName.git"
+    if ($LASTEXITCODE -ne 0) {
+        throw "Failed to add remote"
+    }
+
+    # Enable sparse checkout with cone mode for better performance
+    git sparse-checkout init --cone
+    if ($LASTEXITCODE -ne 0) {
+        throw "Failed to initialize sparse checkout"
+    }
+
+    # Set the sparse checkout patterns - only the directories we need
+    git sparse-checkout set eng/packages/http-client-csharp eng
+    if ($LASTEXITCODE -ne 0) {
+        throw "Failed to set sparse checkout patterns"
+    }
+
+    # Fetch only the main branch with depth 1
+    Write-Host "Fetching $BaseBranch branch with sparse checkout..."
+    git fetch --depth 1 origin $BaseBranch
+    if ($LASTEXITCODE -ne 0) {
+        throw "Failed to fetch repository"
+    }
+
+    # Checkout the fetched branch
+    git checkout $BaseBranch
+    if ($LASTEXITCODE -ne 0) {
+        throw "Failed to checkout $BaseBranch"
+    }
 
     # Create a new branch
     Write-Host "Creating branch $PRBranch..."