[Labels] Make the Ellipses section more clear

Summary:
This patch rewrites the Ellipses section to accomplish two goals:

• Provide clearer guidelines for when to use ellipses and when not to use ellipses
• Correct an error that mistakenly suggested that Configure [something] should not have an ellipsis because it does not require user input; it most certainly does! User input is the whole point, in fact.

Reviewers: VDG, fabianr, romangg

Reviewed By: romangg

Subscribers: abetts

Tags: KDE Human Interface Guidelines

Differential Revision: https://phabricator.kde.org/D14849