Allowing to search users and groups using a begin with filter instead of contains filter

[ldubost]

When running using a value filter, a search can be very slow (minutes) on a large LDAP. By default we should search using value which is going to be extremely faster (LDAP databases are tree indexes) and allow a setting the make a value* search in case the user wants a larger search.

This should apply both to user and groups searches.

[oanalavinia]

Closed by https://github.com/xwikisas/application-ldapuserimport/commit/54daef87ec26e7e67082654405382fee270e1c91

[oanalavinia]

Documentation updated at https://store.xwiki.com/xwiki/bin/view/Extension/ActiveDirectoryApplication#HConfiguringtheUserImport and https://store.xwiki.com/xwiki/bin/view/Extension/ActiveDirectoryApplication#HImportingUsers