fix #5251: login: set autocomplete on password and user

fix #5251: login: set autocomplete on password and user

By default they have 'autocomplete=off'. From [1]:

 > In most modern browsers, setting autocomplete to "off" will not
 > prevent a password manager from asking the user if they would like to
 > save username and password information, or from automatically filling
 > in those values in a site's login form. See the autocomplete
 > attribute and login fields [2].

[1] https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes/autocomplete
[2] https://developer.mozilla.org/en-US/docs/Web/Security/Securing_your_site/Turning_off_form_autocompletion#the_autocomplete_attribute_and_login_fields

Signed-off-by: Maximiliano Sandoval <m.sandoval@proxmox.com>