Add ability to customise localization key path.

[hailwood]

Right now we expect the translation key to be enums.{className}.{value}.
This works well but as applications grow, so too may the number of enums.

Or users may have enums that are part of a module so they may be more localised.

I think we should check if a method public function getTranslationKey(static $value): string exists and if so use the return value from that.
Otherwise it should defaults to how it behaves currently.

We should not move the logic to a method with this name by default.
This is so a user may simply define a trait with this method and use it on their enums.
If we defined this method in our traits then users would be required to tell the enum which of the traits it should use the method from which isn't a great DX.