Add database field for 'Leading Organization' to new Namespace_Settings table

Goal

See: Add property for Leading Organization to user p... (#374017 - closed)

We want to identify and reward Leading Organizations by indicating their status publicly in their profile.

Proposal

Add a user property for Leading Organizations in a table that is not Namespace. The Namespace table is quite large at this moment. A user_details table can be used to add this property.