Syslog for agent logtarget

### Use Case

Currently Telegraf can not write its own log to syslog. Syslog is a standard solution for log collection on many *nix systems.

### Expected behavior

I can specify syslog as agent logtarget and collect log lines in my syslog server.

### Actual behavior

Well, Telegraf doesn't provide such an option.

### Additional info

_No response_

No files, tests, or entry points are named in the issue. Start by locating Telegraf's agent logtarget configuration and current logging implementation, then determine how a syslog target would be configured and validated. Done means an agent can select syslog and its log lines reach a syslog server, with coverage for the new behavior.

Written by the indexing model from the issue text.