calendar-management: Add new-online-calendar page

This is a copy of the existing new-calendar page, but with a
different class name.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/850>

src/gui/calendar-management/meson.build

@@ -9,6 +9,7 @@ blueprints = custom_target(
     'gcal-edit-calendar-page.blp',
     'gcal-new-calendar-page.blp',
     'gcal-new-local-calendar-page.blp',
+    'gcal-new-online-calendar-page.blp',
   ),
   output: '.',
   command: [
@@ -34,4 +35,5 @@ sources += files(
   'gcal-edit-calendar-page.c',
   'gcal-new-calendar-page.c',
   'gcal-new-local-calendar-page.c',
+  'gcal-new-online-calendar-page.c',
 )