Add Bitrate to Dolphin's Additional Information

Summary:
Adds Bitrate to Dolphin's Additional information columns.

BUG: 368418

Test Plan:
Tested in KDE Neon. A bitrate column can be added and shows the bitrate in kb/s:

Works for audio as well as video files!

Reviewers: Dolphin, KDE Applications, broulik, aacid, dfaure, emmanuelp

Reviewed By: Dolphin, KDE Applications, emmanuelp

Subscribers: rkflx, alexeymin, anthonyfieroni

Tags: Dolphin

Differential Revision: https://phabricator.kde.org/D7763