Merge branch 'docs-trigger-keyword-with-variables' into 'master'

Add variables to allowed keywords for trigger jobs

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/101496



Merged-by: Diana Logan <dlogan@gitlab.com>
Approved-by: Diana Logan <dlogan@gitlab.com>
Co-authored-by: Marcel Amirault <mamirault@gitlab.com>