Extract paginated collection gem

refs: CNVS-11648

Test Plan:

Test the sub_accounts api endpoint and make sure the pagination
is not broken.

Change-Id: Ie59674a7a834698ac432307940305d6958cb73f1
Reviewed-on: https://gerrit.instructure.com/31413
QA-Review: Jeremy Putnam <jeremyp@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Simon Williams <simon@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>