Merge branch '439610-default-enable-custom-webhook-template' into 'master'

Enable custom_webhook_template by default

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/145514



Merged-by: Luke Duncalfe <lduncalfe@gitlab.com>
Approved-by: Luke Duncalfe <lduncalfe@gitlab.com>
Approved-by: Ashraf Khamis <akhamis@gitlab.com>
Co-authored-by: Niklas <mc.taucher2003@gmail.com>