[REQ][Java] Enum name should have underscore in case the value is pascal case

Created by: zawataki

Is your feature request related to a problem? Please describe.

If string enum value in OpenAPI definition is pascal case, the enum name on generated Java client will be named without underscores like below:

  public enum StatusEnum {
    WAITINGFORSOMETHING("WaitingForSomething"),

Describe the solution you'd like

I think that should be named with underscores for readability like below:

  public enum StatusEnum {
    WAITING_FOR_SOMETHING("WaitingForSomething"),

Describe alternatives you've considered

Nothing.

Additional context

Nothing.