Add type column to merge_tree_settings in system.settings

Why it matters

This feature improves the usability and clarity of the system settings tables by showing the data type of each setting, helping users understand what kind of values are expected and facilitating better configuration and debugging.

How to use it

Users can query the system.settings and system.merge_tree_settings tables as usual and find the new type column alongside existing columns to see the data type of each setting without any additional configuration.