LDAP: make user-mapping during sync case-insensitive

Problem

When already existing users should be mapped to LDAP the user attribute that is used for the mapping is checked case sensitive because this is how Postgres does queries (this is different on other databases such as MySQL which is not case sensitive). 

The problem is that in OpenOlat the manually created users are always lowercase. A corresponding LDAP user is therefore never found and can not be mapped properly. 

Example: 

• in OO a user with the username "baba" exists. 
• in LDAP the user is identified as "BaBa"
• => mapping is not possible

Normally the LDAP sync then tries to create a new user but fails because the email is already used (if configured to be unique). 

Solution

In the matching of users during LDPA sync the match in OpenOlat should be case-insensitive.

frentix internal: https://office.bexio.com/index.php/pr_project/show/id/273