Support replication for Custom Resource

[jeesmon]

Is your feature request related to a problem? Please describe.
We are in need of replicating istio EnvoyFilter from one namespace to another. As we are using kubernetes-replicator for replicating Secret, ConfigMap, etc. it will be great if we can support EnvoyFilter replication also with replicator. Do you think adding EnvoyFilter replication fits the purpose of this tool? We can look into creating a PR and contribute but wanted to check with community before we start any work.

Describe the solution you'd like
Replicate EnvoyFilter resource created in one namespace to istio-system