Previously, the SiteSetting::Update service allowed to update of a
single site setting. In the About controller, we were using the loop
through all settings -
https://github.com/discourse/discourse/blob/main/app/controllers/admin/config/about_controller.rb#L39
It is suboptimal because if the 3 first settings are saved and the
fourth is invalid, we will end with partially updated data.
Changing SiteSetting::Update to accept hash means that we will check
upfront if none of the settings are hidden or invalid and update all or
none.
Custom policies are used to report which settings are failing.
d50bba3bdc