reduce number of queries for outcome results api endpoint

fixes CNVS-13349

test plan
- regression test outcome results (api and mastery gradebook)

Change-Id: I21080bdacbc5374dc97f940f78f55e6388dfd738
Reviewed-on: https://gerrit.instructure.com/35884
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Drew Bowman <dbowman@instructure.com>
QA-Review: Steven Shepherd <sshepherd@instructure.com>
Product-Review: Joel Hough <joel@instructure.com>