fix: support _lccMuteStatus for conference (#853)

lib/tasks/conference.js

@@ -544,6 +544,13 @@ class Conference extends Task {
     } while (!this.killed && this.conf_hold_status === 'hold');
   }
 
+  /**
+   * mute or unmute side of the call
+   */
+  mute(callSid, doMute) {
+    this.doConferenceMute(this.callSession, {conf_mute_status: doMute});
+  }
+
   /**
    * Add ourselves to the waitlist of sessions to be notified once
    * the conference starts