Continuation of the pull request https://github.com/edx/edx-platform/pull/12226
*Background:* Users often misspell their passwords and can't login a 2d time
*Studio Updates:* None.
*LMS Updates:* an optional "Confirm password" can be shown in the registration form. If the field is present a copy of password must be entered in it.
*Manual test instructions:*
Open http://127.0.0.1:8000/register and try to enter different "Password" and "Confirm password" and see a validation message.