feat(Service Desk): Add endpoints for specific request type data and itd fields (#1592)

* [service_desk] Single request_type method addition
Added new method to fetch single request type.

* [service_desk] Request type fields method addition
Added a method to get field composition of a request type

* [service_desk] Add docs
Added docs for get_request_type and get_request_type_fields methods

* fix: Remove trailing whitespace
Removed the trailing whitespace linted by codacy