new port: security/rubygem-doorkeeper

Doorkeeper is an OAuth 2 provider for Rails and Grape applications

WWW: https://github.com/doorkeeper-gem/doorkeeper

PR: 199817
Differential Revision: https://reviews.freebsd.org/D2494
Submitted by: Torsten Zuehlsdorff <ports@toco-domains.de>
Approved by: mat (mentor)