Implement Custom Resource adapter for GitLab resource
DO NOT MERGE BEFORE !412 (merged) and !468 (merged)
This MR is based on !412 (merged) and uses the generic interfaces to implement a new Custom Resource adapter for GitLab resource. This new adapter will replace the existing adapter.
Related to #429 (closed) and #688
Closes #272 (closed)
Edited by Hossein Pursultani