Add 'sk' (Slovak) to Messenger Widget SDK validation enum

I want the Featurebase Messenger Widget SDK to support the 'sk' (Slovak) language code in the validation enum. Currently, when setting language: 'sk' in the boot function, the SDK returns a validation error: "Invalid enum value. Expected 'bn' | 'bs' | ... | 'sl' | ... received 'sk'". Slovak is available in the dashboard but missing from the SDK's allowed list. This is important so I can provide a localized experience for my Slovak users.