Add sidebar to plugin manager, increase search bar size (#6783)

Co-authored-by: Daniel Beck <1831569+daniel-beck@users.noreply.github.com>
Co-authored-by: Tim Jacomb <21194782+timja@users.noreply.github.com>
Co-authored-by: Basil Crow <me@basilcrow.com>
Co-authored-by: Alexander Brandes <mc.cache@web.de>