Merge branch 'fix_ldap_docs' into 'master'

Clarify LDAP troubleshooting ldap_search example

A customer noted an error/lack of clarity in the LDAP documentation
    with the `ldap_search` example. Previously, if taken literally, the
    customer may have expected the `$` variables to be automatically
    replaced or if they paste the exact `user_filter` contents the
    parentheses would have been incorrect. Let's just simply the filter
    and use exactly what's in the configuration.

See merge request !7489