Better error treatments, webhook payloads and more

Added

• Adjusted some error returns.
• Added the external return webhook to the documentation.
• Improved how the bucket and token replenishment per minute work.
• Added the pixTransactionId in the customer statement endpoint. (https://developers.u4c.com.br/reference/customer-statement)
• Added the customer Balance endpoint. (https://developers.u4c.com.br/reference/customer-balance)

We strongly recommend you:

• Check all error returns from all routes you use and analyze if you have the appropriate handling.
• Check all webhook statuses and ensure you have the appropriate handling.

For more details, please consult our documentation at:
https://developers.u4c.com.br/
https://developers.u4c.com.br/reference/enum-pix-refund
https://developers.u4c.com.br/reference/enum-pix-charge
https://developers.u4c.com.br/reference/enum-pix-transaction
https://developers.u4c.com.br/reference/webhooks-event-types