[Cells 1.0] Sign in/Sign up with an email/password

Seem like duplicate of Login with username and password (#440375 - closed)

Sign-in with an email/password works on Cells 1.0 PoC (&12474 - closed). However, currently to sign in to user account that belong to cell-2 the following action need to be done:

1. Open the browser javascript console and run document.cookie = 'cell_2=true;path=/;domain=gitlab.steveazz.xyz' to force cell-2 logging

As per https://docs.gitlab.com/ee/architecture/blueprints/cells/iterations/cells-1.0.html#questions

UI: The login to Organizations would be scoped to the Organization: https://<GITLAB_DOMAIN>/users/sign_in?organization=gitlab-inc.

On sign in page user should be able select an organization. The sign-in request should contain organization data to allow the router to route the request to correct cell/organization.