add custom header on Refer indicating whether sbc-inbound should fix up the Refer-To

lib/tasks/sip_refer.js

@@ -36,6 +36,7 @@ class TaskSipRefer extends Task {
         method: 'REFER',
         headers: {
           ...this.headers,
+          ...(this.referToIsUri && {'X-Refer-To-Leave-Untouched': true}),
           'Refer-To': referTo,
           'Referred-By': referredBy
         }
@@ -100,6 +101,7 @@ class TaskSipRefer extends Task {
       /* they may have only provided a phone number/user */
       referTo = `sip:${referTo}@${host}`;
     }
+    else this.referToIsUri = true;
     if (!referredBy) {
       /* default */
       referredBy = cs.req?.callingNumber || dlg.local.uri;