Endpoint for ticket's custom statuses

[Medberg212]

Feature Description
When we get a ticket, we get a field "custom_status_id", however, we've got no way to retrieve the custom status's from node-zendesk
The zendesk API provides a way to get those infos :
GET /api/v2/custom_statuses/{custom_status_id}
GET /api/v2/custom_statuses/

Expectations
Add a method to get a ticket custom status's details from it's ID