[Telegram] Don't wait for Telegram to be closed

Summary:
Unlike e.g. kdeconnect-cli telegram stays open after sharing. The Job lives as long as telegram is running,
although the exit code is not interesting. Another window with a useless progress bar is open all the time,
which is especially annoying when using a tiling window manager. This patch waits shortly and stops the job
while keeping telegram open. Directly stopping the job would cause telegram not to open at all. The waiting
time is somewhat ad-hoc, but works well in my case.

Test Plan:
Share something via Telegram. See progress window open shortly and close again. Telegram stays
open, ready to share

Reviewers: apol

Reviewed By: apol

Subscribers: kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D14107