[FIX][REF] do not change auth on web_login handler.
Also, refactored implementation of handler, to pass in context only needed values, instead passing full http params to view template.
This following bug (catched on Odoo v14):
- Website module installed
- Multiple databases available on the host
- When system tries to load menus available on website, it requires user to be set on session (at least public user), but because before this commit, this module changed the auth of login page route to 'none', no user is set in session, which leads to error.