🔨 Add control for custom slugs.

[Pablo Hdez]

• Check if the custom slug already exists.

[David Ponce Vargas]

I would like to work on this 😁.

• Before to create a new link, check if some exist with same slug name.
• If slug name already exist, throw and show the error message.

[Pablo Hdez]

Thanks 💖🥳🥳