Add support for EURid nameserver groups (NS Groups)

[Brianvanwessel]

What does it do?

This PR adds support for EURid nameserver groups (NS Groups) by introducing new request and response classes and extending the domain info response.

Changes

1. Added euridEppUpdateDomainRequest, which supports adding and removing nameserver groups from a domain.
2. Added getNameserverGroups() to euridEppInfoDomainResponse, allowing retrieval of the nameserver groups associated with a domain.
3. Added euridEppInfoNsgroupRequest and euridEppInfoNsgroupResponse, which provide the ability to retrieve detailed information about a nameserver group.

How to test

Domain Update

1. Create an euridEppUpdateDomainRequest.
2. Add and/or remove one or more nameserver groups.
3. Submit the request and verify that the domain's nameserver group assignments are updated successfully.

Domain Info

1. Retrieve a domain using euridEppInfoDomainRequest.
2. Call getNameserverGroups() on the resulting euridEppInfoDomainResponse.
3. Verify that the returned nameserver groups match the domain's configuration.

Nameserver Group Info

1. Create and submit an euridEppInfoNsgroupRequest.
2. Verify that an euridEppInfoNsgroupResponse is returned.
3. Confirm that the response contains the expected information for the requested nameserver group.