Gate plugin feed resolution on token; fall back to portal without it

Author: bachuv

settings.gradle

@@ -1,15 +1,17 @@
 pluginManagement {
-    // Resolve plugins through the Azure Artifacts feed only.
+    // Resolve plugins from the Azure Artifacts feed when its token is available; otherwise the public portal.
     def azfuncFeedToken = System.getenv('AZURE_ARTIFACTS_ENV_ACCESS_TOKEN') ?: providers.gradleProperty('vstsMavenAccessToken').orNull
     repositories {
-        maven {
-            url 'https://pkgs.dev.azure.com/azfunc/public/_packaging/upstream-public/maven/v1'
-            if (azfuncFeedToken) {
+        if (azfuncFeedToken) {
+            maven {
+                url 'https://pkgs.dev.azure.com/azfunc/public/_packaging/upstream-public/maven/v1'
                 credentials {
                     username 'Azure DevOps Services'
                     password azfuncFeedToken
                 }
             }
+        } else {
+            gradlePluginPortal()
         }
     }
 }