Fix #4774: REST registration follows Wekan's setting - #6598

… anyway.

POST /users/register guarded itself with
Accounts._options.forbidClientAccountCreation, which NOTHING IN WEKAN EVER
SETS:

  * the only Accounts.config() call, in server/accounts-common.js, sets
    loginExpirationInDays and nothing else;
  * forbidClientAccountCreation: disableRegistration in config/accounts.js
    is passed to AccountsTemplates.configure() - the useraccounts package's
    own options object, not Meteor's Accounts;
  * and that disableRegistration is only assigned inside an async
    Meteor.call('isDisableRegistration') callback that fires AFTER
    configure() has run, which the file's own comment already records.

So the condition was always falsy and the endpoint never refused anybody.
Turning registration OFF in the Admin Panel closed the sign-up form and
left POST /users/register creating accounts for whoever asked - on an
instance whose administrator had decided nobody else may join. The setting
is read from where it actually lives now, the same way the
isDisableRegistration Meteor method reads it, and a missing Settings
document still means registration is allowed rather than locking a fresh
instance out.

Every call that reaches the refusal is an attempt, because there is no
legitimate caller once the admin has turned registration off, so it is
recorded and shows in Admin Panel / Problems under authz.register /
SignupBleed.

Found while reviewing PR #6598 by AhmedLukman, filed against #4774 - a 403
nobody could reproduce, and which this line cannot produce. Looking for it
turned up the opposite fault.

Nine tests, four of them negative, on a route that had none at all: that
the setting is read where the Meteor method reads it, that the dead Meteor
option is not consulted again AND is still never set anywhere (so a future
change cannot quietly reintroduce two sources of truth that disagree), that
an enabled instance still creates the user and gets its token, and that no
Settings document does not refuse everybody.

Thanks to AhmedLukman and xet7 !