[FEATURE] Automatically relate local users to LDAP

In case a manually created user matches a LDAP user and
LDAP authentication succeeds, it will be automatically
related to the corresponding LDAP user upon login.

Resolves: #60050
Change-Id: Ic639a8adfbc3ab4030251ea4ac2578fa6fd7d896
Reviewed-on: http://review.typo3.org/31320
Reviewed-by: Renaud Fortier <renaud.fortier@fsaa.ulaval.ca>
Tested-by: Renaud Fortier <renaud.fortier@fsaa.ulaval.ca>
Tested-by: Heinz Schilling <webdesign@webtekk.ch>
Reviewed-by: Xavier Perseguers <xavier@typo3.org>
Tested-by: Xavier Perseguers <xavier@typo3.org>