Approver rights for new qtwebchannel maintainer

Arno Rehn is the new maintainer for qtwebchannel. For reference see:

https://lists.qt-project.org/pipermail/development/2020-July/040001.html

At this point, Arno does not have Open Governance approver rights for Qt. Therefore we need a solution whereby he gains maintainer/approver rights for the qtwebchannel repository only (until such time when he becomes a general OGApprover).

Please set up gerrit to facilitate the rights. thank you.