Admin settings for controlling appearance of add cart confirmation popup

Problem/Motivation

Admins would like to control the appearance (size and title) of the add cart confirmation popup. Right now those are hardcoded in the code.

    $title = '';
    $options = ['width' => '700'];

See #2910744: Add a popup confirmation.

Proposed resolution

Create an admin UI setting to control the width and title. This should also provide new permissions for accessing the admin UI.

Remaining tasks

N/A

User interface changes

N/A

API changes

N/A

Data model changes

N/A