Decrease epic issues and child epics page size
What does this MR do?
Decrease max page limit of child epics and epic issues on GraphQL from 2000 to 1000.
It is safe to truncate the limit to 1000 because frontend already limits to this value.
For more information check: https://gitlab.com/gitlab-org/gitlab/-/issues/299814#note_542271775.
Part of https://gitlab.com/gitlab-org/gitlab/-/issues/299814
Edited by Felipe Cardozo