feat: support casting enum values as types

[rickdunkin]

I would like to be able to use the useTypeImports: true option while also mocking enums. I can use the enumsAsTypes: true option, but the enum isn't currently imported as a type, and the string literal isn't typed correctly as the appropriate enum.

I've added a new option castEnumsAsTypes to be used along with enumsAsTypes in order to cast the string values of enums to their correct type. Maybe this shouldn't be a separate option, or perhaps the option should have a different name. I considered having this functionality be the default if both useTypeImports and enumsAsTypes are true, but I went with a new option as I don't know how folks are using this library.

[ardeois]

Thanks for the contribution.
I think there is no need for adding a new option. useTypeImports is quite new and I wouldn't mind to have enums imported as types if useTypeImports and enumsAsTypes are true

[rickdunkin]

The new config option is removed