R1:9632c704c69d

Always allow users to login via email link, even if an install does not use passwords

Summary:
Depends on D20099. Ref T13244. See PHI774. When password auth is enabled, we support a standard email-based account recovery mechanism with "Forgot password?".

When password auth is not enabled, we disable the self-serve version of this mechanism. You can still get email account login links via "Send Welcome Mail" or "bin/auth recover".

There's no real technical, product, or security reason not to let everyone…