Rename subgroup to CRD prefix
This is part of the solution for #1233 (closed). This MR introduces a new value, i.e.
gitlab.operator.crdPrefix, which can be used to add a prefix to GitLab CRD.
This MR depends on !772 (merged). In order to review this MR:
- !772 (merged) must be merged first
- The branch of this MR must be rebased and pushed again to include the realier changes, including GitLab class annotation and Operator v0.5