Rename coredns-crd-plugin to k8gb-core

[kuritka]

• https://github.com/k8gb-io/coredns-crd-plugin

This is a followup from the k8gb.io project meetup (5. October 2022).
The point is that the current coredns-crd-plugin is starting to grow and the
small utility has a bigger scope.

Renaming the coredns-crd-plugin project. Check and modify all build pipelines,
releases, Makefiles, manifests etc... The configuration is k8s_crd {....}.
Consider configuration k8gb_core {....}