* fix: Fix ruby client generator to generate setter methods with not null validation
Not null validation was missing for required and non-nullable properties when
no other validation was present.
* fix: Fix an issue where the initialize method did not accept attributes defined in its parent class
* [Ruby] Fix Operation Servers
* user `server_index` instead of `index`
* use nil as default
* add tests
* revert tests
* add tests to custom file
* add test file to ruby-faraday
