* Users: add is_disabled column

* Users: disable users removed from LDAP

* Auth: return ErrInvalidCredentials for failed LDAP auth

* User: return isDisabled flag in user search api

* User: mark disabled users at the server admin page

* Chore: refactor according to review

* Auth: prevent disabled user from login

* Auth: re-enable user when it found in ldap

* User: add api endpoint for disabling user

* User: use separate endpoints to disable/enable user

* User: disallow disabling external users

* User: able do disable users from admin UI

* Chore: refactor based on review

* Chore: use more clear error check when disabling user

* Fix login tests

* Tests for disabling user during the LDAP login

* Tests for disable user API

* Tests for login with disabled user

* Remove disable user UI stub

* Sync with latest LDAP refactoring