For Security Code Mauve: #13439

A couple of problems in current rbac code:

• All the logic (rbac filter, envoy matcher, rbac policy, etc.) are tightly coupled in rbac.go, making it very hard to extend and find out the relationship between policy and generated config
• The unit test rbac_test.go is full of boilerplate and extreme hard to read and maintain (2000 lines of code). It's super hard to find out what is covered and what is not
• The current e2e test doesn't cover all the use cases, like the ClusterRbacConfig is not fully tested, etc.

/cc @liminw @pitlv2109