Allow for a admin level setting for global default for full-width pages using fabric editor

Currently, only a user level setting exists to enable full width pages, as addressed in the linked duplicate issue: CONFCLOUD-67503

Admins would like the ability to enable this as a global setting, effectively creating full width default for all page creation. 

 
Hello Everyone,

There is now an admin setting to default new pages to be full-width at the site level. Only site admins can update this setting.

Thanks,

Niraj