new port: textproc/rubygem-html-pipeline-gitlab

Rubygem containing extension filters for html-pipeline used by GitLab

WWW: https://gitlab.com/gitlab-org/html-pipeline-gitlab

PR: 199917
Differential Revision: https://reviews.freebsd.org/D2529
Submitted by: Torsten Zuehlsdorff <ports@toco-domains.de>
Reviewed by: mat (mentor)