feat: [Request] Event on QKnob with current dragging value quasarframework#2004

Add "@drag-value" event

Author: rstoenescu

src/components/knob/QKnob.js

@@ -183,6 +183,9 @@ export default {
       if (this.model !== value) {
         this.model = value
       }
+
+      this.$emit('drag-value', value)
+
       if (this.value === value) {
         return
       }