Keytar and UIKind Azure Authentication (#9743)

* Handle webmode

* Fix keytar

* Specify that it can be null too.

* Configuraiton option

* Fix callback URL

* Update message, only show if the user is on Linux

* Change message

extensions/azurecore/package.json

@@ -81,6 +81,12 @@
             "type": "boolean",
             "default": false,
             "description": "%config.enableArcFeatures%"
+          },
+          "azure.noSystemKeychain": {
+            "type": "boolean",
+            "default": false,
+            "description": "%config.noSystemKeychain%",
+            "when": "isLinux || isWeb"
           }
         }
       }