[docs] draft for an upgrade guide from 2.4 to 3.0
different error for nop public parent
do still display publish button if not published successfully
Merge pull request #2814 from Chive/docs/upgrade

[docs] upgrade guide from 2.4 to 3.0
increase queries for edit mode
Merge pull request #2831 from digi604/fix-2821

Fix #2821 (pending pages no error messages)
fixes #2827
cleanup
fix tests
Merge pull request #2835 from digi604/fix-2827

fixes #2827 (moving public pages to unpublished parents)