add global environment variable feature

packages/node_modules/@node-red/runtime/lib/flows/index.js

@@ -777,6 +777,16 @@ const flowAPI = {
 }
 
 
+function getGlobalConfig() {
+    let gconf = null;
+    eachNode((n) => {
+        if (n.type === "global-config") {
+            gconf = n;
+        }
+    });
+    return gconf;
+}
+
 module.exports = {
     init: init,
 
@@ -790,6 +800,9 @@ module.exports = {
     get:getNode,
     eachNode: eachNode,
 
+
+    getGlobalConfig: getGlobalConfig,
+    
     /**
      * Gets the current flow configuration
      */