Added payload to bot_started update

Author: achuprin

schema.yaml

@@ -2358,6 +2358,12 @@ components:
               description: User pressed the 'Start' button
               allOf:
                 - $ref: '#/components/schemas/User'
+            payload:
+              description: Additional data from deep-link passed on bot startup
+              type: string
+              maxLength: 512
+              nullable: true
+              readOnly: false
           required:
             - chat_id
             - user