chore: update NuGet.config files in examples

Author: alestoya

Telerik.Examples.ContentSecurityPolicy/NuGet.Config

@@ -4,4 +4,10 @@
 		<add key="nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
 		<add key="Telerik" value="https://nuget.telerik.com/v3/index.json" />
 	</packageSources>
+	<packageSourceCredentials>
+    <Telerik>
+      <add key="Username" value="api-key" />
+      <add key="ClearTextPassword" value="%TELERIK_NUGET_KEY%" />
+    </Telerik>
+  </packageSourceCredentials>
 </configuration>

Telerik.Examples.Mvc/NuGet.Config

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+	<packageSources>
+		<add key="nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
+		<add key="Telerik" value="https://nuget.telerik.com/v3/index.json" />
+	</packageSources>
+	<packageSourceCredentials>
+    <Telerik>
+      <add key="Username" value="api-key" />
+      <add key="ClearTextPassword" value="%TELERIK_NUGET_KEY%" />
+    </Telerik>
+  </packageSourceCredentials>
+</configuration>

Telerik.Examples.RazorPages/NuGet.config

@@ -5,5 +5,11 @@
 		<add key="nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
         <add key="Telerik" value="https://nuget.telerik.com/v3/index.json" />
     </packageSources>
+    <packageSourceCredentials>
+    <Telerik>
+      <add key="Username" value="api-key" />
+      <add key="ClearTextPassword" value="%TELERIK_NUGET_KEY%" />
+    </Telerik>
+  </packageSourceCredentials>
 </configuration>