preload enrollment term for account course index

refs CNVS-11420

Change-Id: Icebecea5e5444d7b75dfcb193f947278aab3fe21
Reviewed-on: https://gerrit.instructure.com/31014
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Nick Cloward <ncloward@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>