Allow Use of Same VAT/Tax Registration Number for Multiple Suppliers

The system currently prevents the registration of multiple suppliers sharing the same VAT/Tax Registration Number by throwing a duplication error. However, the business requires the ability to register suppliers with identical VAT/Tax IDs due to specific tax and legal requirements, especially for companies operating in Dubai. In this region, it is common for parent-child supplier relationships to share the same VAT/Tax Registration Number, making it a legitimate and necessary scenario. This issue occurs both at the header level when try to update the same Tax registration number & during supplier registration and when suppliers use the self-registration link or while