Syslog-NG: better explain the related templates

[AdSchellevis]

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• I have read the contributing guide lines at https://github.com/opnsense/docs/blob/master/CONTRIBUTING.md
• I have searched the existing issues and I am convinced that mine is new.

Is your feature request related to a problem? Please describe.

The syslog-ng plugin system came with some additional files which eventually replaces the legacy syslog plugin system, apparently we forgot to explain how to add additional sockets for jails, which is within the legacy (clog) system handled with the local keyword.

Describe the solution you like

Describe the new files, probably combine information available in GitHub into a more consistent guideline how to add new log targets and sources. If clog is being deprecated, probably best to remove the current legacy description as well for clarity.

Describe alternatives you considered

Additional context

opnsense/plugins#2587 (comment)