fix: SQL errors as response messages

[PedroChaparro]

It seems that the API is returning SQL errors in JSON responses. For instance, when I create a duplicated user, I receive the following error from the Gateway:

{
  return: {
    code: 500,
    error: true,
    msg: 'ERROR: duplicate key value violates unique constraint "users_username_key" (SQLSTATE 23505)'
  }
}

I believe it would be better if you return a specific error code like 409 (Conflict) and a custom error message such as "The username is already in use." At least in this case. Otherwise, clients will be forced to display a generic error like "There was an error creating your account," and the user will never know what the problem is.

[PedroChaparro]

What do you think? @Woynert, @shoriwe 🤔

[Woynert]

I agree, this is important for user experience.