allow to activate/deactivate the progress indicator on task bar entry

Summary:
the Elisa application menu has an entry to activate or deactivate the
reporting of progress on the task bar entry (currently supported on
Plasma, Windows and linux environments supporting
com.canonical.Unity.LauncherEntry .

BUG: 406454

Test Plan: One can activate or deactive the progress reporting

Reviewers: #elisa, ngraham

Differential Revision: https://phabricator.kde.org/D20636