Update an existing account holder.

POST {{baseUrl}}/updateAccountHolder

This endpoint is used to update the accountHolderDetails or processingTier of an account holder.

If updating the accountHolderDetails, only the details which have been provided will be updated. Other details will be left as-is with the exception of the following fields: * accountHolderDetails.address * accountHolderDetails.fullPhoneNumber * accountHolderDetails.bankAccountDetails.BankAccountDetail * accountHolderDetails.businessDetails.shareholders.ShareholderContact, which requir