[Updates page] Add text to the checkbox instead of putting it in a separate label

Test Plan: Works fine and clicking on the text now toggles the checkbox.

Reviewers: apol, #discover_software_store, broulik

Reviewed By: apol, #discover_software_store

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D24712