Summary:
Since now overlaysheets have the header always visible when there is a
close button, put the write review button in there so that's always
visible itself and the layout looks cleaner

Test Plan:
Before:
{F8209177}

After:
{F8209181}

Reviewers: #discover_software_store, ngraham

Reviewed By: #discover_software_store, ngraham

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D28474