Add x-enumNames to Enum schema

[jimmyl0l3c]

Add x-enumNames to enums similarly to NSwag.

Motivation

I use django-simple-history that has enum of diff types (+=added, -=removed, ~=changed) and ng-openapi-gen for generating DTOs. The problem is, the generator generates the enum member names based on the value, but in this case it generates invalid enum, because the values are only special characters.

By adding the x-enumNames extension, the generator can use those.

[tfranzel]

Hi, thanks for the PR. Unfortunately, this has no widespread support (swagger-api/swagger-ui#5272) even though I like the concept.

I'm not in favor of adding stuff to the core code that only has marginal support and could very well be superseded by another proposal making this a unnecessary technical dept.