Add default values for settings in `ducklake_metadata` page

[gahtan-syarif]

Perhaps its a good idea to add default values for the settings specified in ducklake_metadata? So that different engines implementing the ducklake format wouldn't implement different default values. Iceberg specifies their default values like this

Note: the configuration page does specify the default values for some settings, but these are specific to the duckdb extension, not the format as a whole.

[guillesd]

This is in my backlog @gahtan-syarif !