coredns CRD plugin

[ytsarev]

We can try to implement coredns CRD plugin conceptually similar to coredns/coredns#1999

It should enable coredns to read data directly from DNSEndpoint CRD object.

It will get rid us of a whole class of problems of etcd maintenance like the one in #220
and seriously increase reliability of the system by reduction of 3 components:

• etcd-operator
• etc itself
• internally facing external-dns ( I know it sounds weird, but that exactly how it works now:)

It can be either a separate plugin or extension of the current kubernetes one

[ytsarev]

Solved by https://github.com/AbsaOSS/k8s_crd and https://github.com/AbsaOSS/k8gb/pull/292
Kudos to @k0da !