We should not create a pet if birthdate is empty

As user, I want to avoid pet's registration when birthdate is empty so that I can be sure every pet has a valid birthdate

Acceptance Criteria

• I can see a message in English saying "We should provide a valid birthdate" when birthdate data is empty
• I can see a message in Spanish saying "Debemos proporcionar una fecha de nacimiento en el pasado" when birthdate data is empty
• I can see test updated / added to cover this functionality
• All tests passing

References

• https://github.com/josdem/vetlog-spring-boot/blob/bbe4393bc5a8fb16297a56cfb5c7909c80ceae2b/src/main/java/com/josdem/vetlog/binder/PetBinder.java#L50L51
• https://github.com/josdem/vetlog-spring-boot/blob/bbe4393bc5a8fb16297a56cfb5c7909c80ceae2b/src/main/java/com/josdem/vetlog/controller/PetController.java#L127L142