Add NuGet.config to test projects to fix nuget restore under network isolation

The VerifyImagesWithWebApps tests fail because nuget restore inside test
containers cannot reach api.nuget.org due to 1ES Pipeline Template network
isolation. Added NuGet.config files pointing to the Azure DevOps public feed
to all test project directories that use nuget restore in their Dockerfiles.

Co-authored-by: lbussell <36081148+lbussell@users.noreply.github.com>

Author: Copilot

tests/Microsoft.DotNet.Framework.Docker.Tests/projects/dotnetapp-4.8.1/NuGet.config

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <packageSources>
+    <clear />
+    <add key="dotnet-public" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-public/nuget/v3/index.json" />
+  </packageSources>
+</configuration>

tests/Microsoft.DotNet.Framework.Docker.Tests/projects/dotnetapp-4.8/NuGet.config

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <packageSources>
+    <clear />
+    <add key="dotnet-public" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-public/nuget/v3/index.json" />
+  </packageSources>
+</configuration>

tests/Microsoft.DotNet.Framework.Docker.Tests/projects/webapp-4.6.2/NuGet.config

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <packageSources>
+    <clear />
+    <add key="dotnet-public" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-public/nuget/v3/index.json" />
+  </packageSources>
+</configuration>

tests/Microsoft.DotNet.Framework.Docker.Tests/projects/webapp-4.7.1/NuGet.config

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <packageSources>
+    <clear />
+    <add key="dotnet-public" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-public/nuget/v3/index.json" />
+  </packageSources>
+</configuration>

tests/Microsoft.DotNet.Framework.Docker.Tests/projects/webapp-4.7.2/NuGet.config

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <packageSources>
+    <clear />
+    <add key="dotnet-public" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-public/nuget/v3/index.json" />
+  </packageSources>
+</configuration>

tests/Microsoft.DotNet.Framework.Docker.Tests/projects/webapp-4.7/NuGet.config

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <packageSources>
+    <clear />
+    <add key="dotnet-public" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-public/nuget/v3/index.json" />
+  </packageSources>
+</configuration>

tests/Microsoft.DotNet.Framework.Docker.Tests/projects/webapp-4.8.1/NuGet.config

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <packageSources>
+    <clear />
+    <add key="dotnet-public" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-public/nuget/v3/index.json" />
+  </packageSources>
+</configuration>

tests/Microsoft.DotNet.Framework.Docker.Tests/projects/webapp-4.8/NuGet.config

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <packageSources>
+    <clear />
+    <add key="dotnet-public" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-public/nuget/v3/index.json" />
+  </packageSources>
+</configuration>