Summary:
The two patches D10577 and D10687 modified some config entries for
sidebar and statusbar states.
This patch adds an update files for kconf_update to migrate the
old settings.

Test Plan:
Manual test with `kconf_update gwenview.upd` converts
`~/.config/gwenviewrc`. Hint: There can be different versions of
`kconf_update` on a system, take care to use the kf5 version.
Tested with `make install` to automatically update by KDE.

Reviewers: #gwenview, rkflx

Reviewed By: #gwenview, rkflx

Subscribers: rkflx

Differential Revision: https://phabricator.kde.org/D10689