REPP: bulk ns change - add an option to add new ns

[vohmar]

registrar has requested for an option to add new nameserver record to many domains.

Maybe we could solve this by making the id parameter optional in the bulk ns change request
https://internetee.github.io/repp-apidoc/#bulk-nameserver-change

so if id is missing or blank than nameservers from the attributes block is just added to the list of domains

Requires changes in REPP and repp-doc + possibly in registrar