Adding a new item to Extension General Setting

Hi folks,

I’d be more than happy of someone describes, what is the process of adding a new item to Extension General Settings. I’ve planning to add a call restriction field to my SIP extensions, so admins can restrict call duration for specific extensions.

I searched but didnt find anything in the GUI, thought it might be an idea to add it to the GUI but need some info on contribution rules and methods.

Sorry if my question does not comply with forum rules.