add logging.json setting (#34581)

docs/setup/settings.asciidoc

@@ -131,6 +131,12 @@ be lowercase, and conform to {es} {ref}/indices-create-index.html[index name lim
 `logging.dest:`:: *Default: `stdout`* Enables you specify a file where Kibana
 stores log output.
 
+`logging.json:`:: *Default: false* Logs output as JSON. When set to `true`, the 
+logs will be formatted as JSON strings that include timestamp, log level, context, message 
+text and any other metadata that may be associated with the log message itself. 
+If `logging.dest.stdout` is set and there is no interactive terminal ("TTY"), this setting
+will default to `true`.
+
 `logging.quiet:`:: *Default: false* Set the value of this setting to `true` to
 suppress all logging output other than error messages.