Add translations not handled by Statamic but by the default Laravel app

[helloDanuk]

There are a few translations that are handled by the default Laravel app, not by Statamic. i.e the password reset validation error messages:

It might be worth to mention in the docs how to translate them. As it would be weird for the rest of the Statamic CP to be translated but not for the authentication stuff to be.

See https://github.com/statamic/cms/issues/2512 for more information.