Module getent is missing from documentation

[FiZiX]

Incorrect section

getent module is no longer documented here: https://syslog-ng.github.io/admin-guide/110_Template_and_rewrite/000_Customize_message_format/007_Template_functions_of_syslog-ng

Description of the problem

Description and usage of getent module is missing.

Proposed solution

Port documentation from previous version. One example is available here: https://web.archive.org/web/20240415154756/https://www.syslog-ng.com/technical-documents/doc/syslog-ng-open-source-edition/3.16/administration-guide/58

[HofiOne]

@zsoltgyulai94 could you please add the missing part? thank you!