Add named-formatter to the syslog-handler

The syslog handler supports adding a formatter. Currently in WildFly only the log message itself is added as the message for the payload. Users may want to include other attributes such as the thread or an MDC entry. We should allow any formatter to be assigned to the syslog handler for formatter the message portion of the syslog payload.

This should be as simple as adding a named-formatter attribute to the syslog-handler resource.

Tests will be done in the current syslog handler tests.

Community documentation will be handled my Wildscribe since this is just a common attribute which is already present on most other handlers.