Single/Double Click Option at Workspace KCM

Summary:
This patch adds the single/double click option to
the Workspace KCM.

BUG: 393547
BUG: 377310

Reviewers: romangg, ngraham, #plasma, mart

Reviewed By: romangg, #plasma, mart

Subscribers: mart, davidedmundson, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D12946