chore: Swagger documentation for contact labels APIs (#8279)

Co-authored-by: Sojan Jose <sojan@pepalo.com>

swagger/definitions/index.yml

@@ -168,6 +168,8 @@ contact_conversations:
       - $ref: '#/definitions/conversation'
       - $ref: ./resource/extension/contact/conversation.yml
       - $ref: ./resource/extension/conversation/with_display_id.yml
+contact_labels:
+  $ref: ./resource/extension/contact/labels.yml
 
 ## conversation
 conversation_list:

swagger/definitions/resource/extension/contact/labels.yml

@@ -0,0 +1,7 @@
+type: object
+properties:
+  payload:
+    type: array
+    description: Array of labels
+    items:
+      type: string