Natively support OCM on EKS

[jaswalkiranavtar]

Describe the enhancement
Currently OCM supports x509 certificates based authenticated only which is not supported by EKS. Hence, we request the csr controller on the hub and certificateController on the managed cluster to be extracted such that those controllers can be swapped by different vendor specific controllers leading to support on all platforms without making further changes to OCM code.

@qiujian16 has proposed a regsitration-driver based solution.

[mikeshng]

@qiujian16 shared this initial design doc:
https://docs.google.com/document/d/1HZG1mfHyAmjETjLK5ccE0tspCiXkTBmTzwMxzp6alL8/edit

[mikeshng]

Qiu Jian's registration refactor WIP PR that is related to this issue: #535

[jaswalkiranavtar]

Created a formal enhancement proposal for supporting ocm natively on eks

https://github.com/open-cluster-management-io/enhancements/pull/125/files