Add ability to enable JSON logging only

Why it matters

This feature allows users to configure JSON formatting selectively on individual logging channels such as syslog, console, errorlog, or the default log. It helps in isolating and customizing log outputs to improve log management and integration with external systems.

How to use it

To enable JSON logging for a specific channel, set the logger.formatting.channel configuration parameter to one of the following values: syslog, console, errorlog, or log. This directs ClickHouse to format logs in JSON only for the chosen channel.