preload pseudonyms for enrollments api fixes #9385
preload pseudonyms for enrollments api fixes #9385

avoids N+1 queries

test plan:
 * run specs for enrollments api

Change-Id: I8704677379521a42fbaf5c0f3c06ccb6b88f6806
Reviewed-on: https://gerrit.instructure.com/12118
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
Reviewed-by: Brian Palmer <3cb4e1df5ec4da2c7c4af7c52cec8cf340a55a10@instructure.com>

Rvor/canvas-lms,fronteerio/canvas-lms,utkarshx/canvas-lms,arrivu/hoodemo,nditech/red-innovadores-lms,arrivu/arrivu-lms,sli7246/canvas_branch,skmezanul/canvas-lms,va7map/canvas-lms,venturehive/canvas-lms,sfu/canvas-lms,roxolan/canvas-lms,rup/Tarrax,Unow/canvas-lms,tgroshon/canvas-lms,jay3126/canvas-lms,jay3126/canvas-lms,redconfetti/canvas-lms,arrivu/jigsaw-lms,Unow/ins,grahamb/canvas-lms,Unow/canvas-lms,merichar/canvas-lms,fronteerio/canvas-lms,landonwilkins/canvas-lms,sli7246/canvas_branch,wye0220/shindig-canvas,juoni/canvas-lms,grahamb/canvas-lms,sfu/canvas-lms,shidao-fm/canvas-lms,landonwilkins/canvas-lms,venturehive/canvas-lms,greyhwndz/canvas-lms,HotChalk/canvas-lms,whalejasmine/canvas-lms,ankithbti/canvas_lms,sfu/canvas-lms,djbender/canvas-lms,grahamb/canvas-lms,arrivu/jigsaw-lms,redconfetti/canvas-lms,kyroskoh/canvas-lms,antoniuslin/canvas-lms,sfu/canvas-lms,Jyaasa/canvas-lms,ShreniiNepal/shrenii_lmp,wrdsb/canvas-lms,samuels410/greatlakes-lms,djbender/canvas-lms,tgroshon/canvas-lms,Jyaasa/canvas-lms,redconfetti/canvas-lms,SwinburneOnline/canvas-lms,Rvor/canvas-lms,SwinburneOnline/canvas-lms,wrdsb/canvas-lms,grahamb/canvas-lms,utkarshx/canvas-lms,djbender/canvas-lms,efrj/canvas-lms,juoni/canvas-lms,efrj/canvas-lms,arrivu/jigsaw-lms,SwinburneOnline/canvas-lms,wimemx/Canvas,wye0220/shindig-canvas,loganrun/pincan,venturehive/canvas-lms,Unow/ins,fronteerio/canvas-lms,skmezanul/canvas-lms,HotChalk/canvas-lms,sfu/canvas-lms,venturehive/canvas-lms,fronteerio/canvas-lms,ShreniiNepal/shrenii_lmp,va7map/canvas-lms,wrdsb/canvas-lms,arrivu/qibla-ecampus,samuels410/greatlakes-lms,antoniuslin/canvas-lms,roxolan/canvas-lms,antoniuslin/canvas-lms,arrivu/arrivu-lms,Rvor/canvas-lms,landonwilkins/canvas-lms,shidao-fm/canvas-lms,greyhwndz/canvas-lms,kyroskoh/canvas-lms,utkarshx/canvas-lms,leftplusrightllc/canvas-lms,skmezanul/canvas-lms,loganrun/pincan,samuels410/greatlakes-lms,parbros/red-innovadores-lms,wrdsb/canvas-lms,tgroshon/canvas-lms,usmschuck/canvas,leftplusrightllc/canvas-lms,HotChalk/canvas-lms,sfu/canvas-lms,redconfetti/canvas-lms,usmschuck/canvas,whalejasmine/canvas-lms,sdeleon28/canvas-lms,juoni/canvas-lms,arrivu/arrivu-lms,shidao-fm/canvas-lms,ShreniiNepal/shrenii_lmp,nditech/red-innovadores-lms,nditech/red-innovadores-lms,efrj/canvas-lms,merichar/canvas-lms,sdeleon28/canvas-lms,sdeleon28/canvas-lms,parbros/red-innovadores-lms,tgroshon/canvas-lms,greyhwndz/canvas-lms,wimemx/Canvas,usmschuck/canvas,roxolan/canvas-lms,SwinburneOnline/canvas-lms,sdeleon28/canvas-lms,ankithbti/canvas_lms,leftplusrightllc/canvas-lms,antoniuslin/canvas-lms,greyhwndz/canvas-lms,nditech/red-innovadores-lms,arrivu/hoodemo,landonwilkins/canvas-lms,kyroskoh/canvas-lms,Jyaasa/canvas-lms,wye0220/shindig-canvas,jay3126/canvas-lms,loganrun/pincan,utkarshx/canvas-lms,shidao-fm/canvas-lms,Unow/canvas-lms,sli7246/canvas_branch,merichar/canvas-lms,skmezanul/canvas-lms,Unow/ins,efrj/canvas-lms,Rvor/canvas-lms,kyroskoh/canvas-lms,Jyaasa/canvas-lms,rup/Tarrax,samuels410/greatlakes-lms,arrivu/qibla-ecampus,juoni/canvas-lms,sfu/canvas-lms,whalejasmine/canvas-lms,grahamb/canvas-lms,jay3126/canvas-lms,arrivu/qibla-ecampus,HotChalk/canvas-lms,rup/Tarrax,leftplusrightllc/canvas-lms,roxolan/canvas-lms,arrivu/hoodemo,va7map/canvas-lms,ShreniiNepal/shrenii_lmp,va7map/canvas-lms,djbender/canvas-lms,whalejasmine/canvas-lms,usmschuck/canvas,parbros/red-innovadores-lms,ankithbti/canvas_lms,wimemx/Canvas