Try uncommenting the lines for the search user:
#  $Self->{'Customer::AuthModule::LDAP::SearchUserDN'} = 'otrsldap';
#  $Self->{'Customer::AuthModule::LDAP::SearchUserPw'} = 'password';

Should be:
$Self->{'Customer::AuthModule::LDAP::SearchUserDN'} = 'otrsldap';
$Self->{'Customer::AuthModule::LDAP::SearchUserPw'} = 'password';