Move Snowdrop Istio extension to Fabric8 Kubernetes Client Extensions

[rohanKanojia]

We have Istio Java Client Extension which is based on Fabric8 Kubernetes Client hosted here: https://github.com/snowdrop/istio-java-api

This was created by @metacosm and @iocanel due to their teaming requiring working with Istio API at the time of creation. Since now we have got Fabric8 Kubernetes Client Extensions for Knative, Tekton, Service Catalog, CertManager, VolumeSnapshot in extensions/ module. It would be better if This istio extension could be moved to the Fabric8 Kubernetes Client repository. Having this extension in a separate repository requires consistent maintenance effort regarding updating kubernetes-client version from time to time.

I had created a similar issue on the Snowdrop repository in past regarding this as well: snowdrop/istio-java-api#117

We need to decide how we want to proceed with this migration. @cmoulliard @metacosm @iocanel Would appreciate it if you could share your thoughts on this.