resource/gitlab_project_approval_rule: fix potential accidental destroy of resource if not in first page
This fixes a potential bug that the resource is marked for destroy after a read, because it was not found on the first page. Pagination was not implemented. However, there exist a specific API to get a single project-level approval rule. I have implemented it in go-gitlab:
After it is released, we should be able to just rebase and LGTM ;)
Refs: #949 (closed)