Fix Secure Supply Chain compliance issues (#11548)

## Description

Resolves Secure Supply Chain warnings.

### Type of Change
- Bug fix (non-breaking change which fixes an issue)

### Why

To meet compliance requirements.

Closes #11209
Closes #10374

### What

* Removed invalid `nuget.config` configurations
* Removed unnecessary `.npmrc` files
* Temporarily left nuget.org feed in config (tracking: #11557)

## Screenshots
N/A

## Testing
N/A

Author: jonthysell

.gitignore

@@ -33,6 +33,12 @@ node_modules
 # Optional REPL history
 .node_repl_history
 
+# No NPM config to pass CFS compliance
+.npmrc
+
+# We use yarn, not npm
+package-lock.json
+
 #React Native
 *AppPackages*
 *BundleArtifacts*

NuGet.Config

@@ -4,5 +4,11 @@
     <add key="enabled" value="True" />
     <add key="automatic" value="True" />
   </packageRestore>
-  <!-- Note: Do not specify any NuGet feeds in this file, everything is available on the fallback NuGet.org. -->
+  <packageSources>
+    <clear />
+    <!-- Warning: Never add more NuGet feeds, to be compliant this repo must only rely on this single ADO feed. -->
+    <add key="react-native" value="https://pkgs.dev.azure.com/ms/react-native/_packaging/react-native-public/nuget/v3/index.json" />
+    <!-- Remove (comment out) the nuget.org feed once our ADO feed is configured correctly. See https://github.com/microsoft/react-native-windows/issues/11557 -->
+    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
+  </packageSources>
 </configuration>

change/react-native-windows-14a87dda-f285-4cd4-8a0f-b5aa9543cb9f.json

@@ -0,0 +1,7 @@
+{
+  "type": "prerelease",
+  "comment": "Fix Secure Supply Chain compliance issues",
+  "packageName": "react-native-windows",
+  "email": "[email protected]",
+  "dependentChangeType": "patch"
+}