Trigger cicd pipeline after merge request accept on master, Gitlab

Trying to run some task after merge request get accept (only on master branch).
I am aware of only: - master -merge_requests config options, but want to specifically run pipeline only when code get merged in master.

https://docs.gitlab.com/ee/ci/yaml/

https://gitlab.com/gitlab-org/gitlab-ce/issues/31296#note_34944784

integration-testing:
  stage: test
  only:
    - master
  script:
    - ./gradlew clean build asciidoctor

Another option is to create a webhook

https://gitlab.scm.webanywhere.co.uk/help/user/project/integrations/webhooks.md

If the "Merge request events" is clicked one could trigger a pipeline if a Pull Request gets updated, created or merged.

StackExchange DevOps Q#8629, answer score: 1