Move embedded screenshot from to-be-retired wiki.gnome.org to GitLab repository
Per https://discourse.gnome.org/t/wiki-gnome-org-retirement-feedback-wanted/17314/28
Image should probably be moved in GitLab code repository and called via https://gitlab.gnome.org/GNOME/$reponame/-/raw/$branchname/path/to/image/$imagename.png
./gnote/data/org.gnome.Gnote.appdata.xml.in: <image width="872" height="637">https://wiki.gnome.org/Apps/Gnote?action=AttachFile&do=get&target=gnote_main_window.png</image>
./gnote/data/org.gnome.Gnote.appdata.xml.in: <image width="872" height="637">https://wiki.gnome.org/Apps/Gnote?action=AttachFile&do=get&target=start_here.png</image>
./gnote/data/org.gnome.Gnote.appdata.xml.in: <image width="872" height="637">https://wiki.gnome.org/Apps/Gnote?action=AttachFile&do=get&target=using_links.png</image>