add label to tts stt spans (#909)

Co-authored-by: Markus Frindt <m.frindt@cognigy.com>

lib/tasks/gather.js

@@ -1053,6 +1053,7 @@ class TaskGather extends SttTask {
 
     this.span.setAttributes({
       channel: 1,
+      'stt.label': this.label || 'None',
       'stt.resolve': reason,
       'stt.result': JSON.stringify(evt)
     });