Customize payload of webhook

From user (riad):
Is there away to customize the payload of the webhook? for example the create a new key in the payload and assign it the value of 'ref' key. I am using the webhook to trigger a pipeline in gitlab cicd and rely on the value of 'ref' of the payload to decide whever or not to the job. The problem is gitlab updates the value of this key.
This is the original payload:
``` {'ref': 'refs/heads/master', 'head': 'f4d5h9hoodq3qs4pvk895548uko5f9rb', 'prev': '3mvq8oii4h050elhsfu38qe6etshcnbf', 'repository': {'name': 'checks-dev', 'owner': 'riad'}}```
here what is being received in gitlab: ```{"ref":"issue3","head":"f4d5h9hoodq3qs4pvk895548uko5f9rb","prev":"3mvq8oii4h050elhsfu38qe6etshcnbf","repository":{"name":"checks-dev","owner":"riad"},"id":"25062774","variables":{}}```

No source file, test, or entry point is identified in the issue. Start by tracing webhook payload construction and the GitLab CI/CD delivery path, then determine how a caller could request an additional key while preserving the original ref. Done means the customization behavior is specified and verified with a GitLab-delivered payload.

Written by the indexing model from the issue text.