add subject to conversation html email notification
add subject to conversation html email notification

fixes CNVS-14220

test plan
- cause a conversation message notification to be sent
- check the html email notification that was sent
- ensure that the conversation subject appears in the message

Change-Id: Ie2e1c7cb2865e2cb9a1ac1763ade2eebd88dc373
Reviewed-on: https://gerrit.instructure.com/37716
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
Reviewed-by: Matthew Wheeler <ce71fbafda91d6c8f12582e1837687d5fe592dd9@instructure.com>
Product-Review: Matthew Wheeler <ce71fbafda91d6c8f12582e1837687d5fe592dd9@instructure.com>
Tested-by: Matthew Wheeler <ce71fbafda91d6c8f12582e1837687d5fe592dd9@instructure.com>
QA-Review: Steven Shepherd <e794458448443812fb2685675aab3bbd1a3891bc@instructure.com>

Unow/canvas-lms,skmezanul/canvas-lms,utkarshx/canvas-lms,venturehive/canvas-lms,skmezanul/canvas-lms,SwinburneOnline/canvas-lms,snehakachroo1/LSI_replica,snehakachroo1/LSI_replica,greyhwndz/canvas-lms,wrdsb/canvas-lms,greyhwndz/canvas-lms,AndranikMarkosyan/lms,skmezanul/canvas-lms,Jyaasa/canvas-lms,SwinburneOnline/canvas-lms,Rvor/canvas-lms,whalejasmine/canvas-lms,grahamb/canvas-lms,roxolan/canvas-lms,jay3126/canvas-lms,leftplusrightllc/canvas-lms,redconfetti/canvas-lms,sfu/canvas-lms,utkarshx/canvas-lms,efrj/canvas-lms,wye0220/shindig-canvas,fronteerio/canvas-lms,eCNAP/CANVAS,instructure/canvas-lms,sfu/canvas-lms,Jyaasa/canvas-lms,skmezanul/canvas-lms,instructure/canvas-lms,djbender/canvas-lms,HotChalk/canvas-lms,eCNAP/CANVAS,whalejasmine/canvas-lms,wye0220/shindig-canvas,sdeleon28/canvas-lms,narigone/canvas,juoni/canvas-lms,va7map/canvas-lms,efrj/canvas-lms,utkarshx/canvas-lms,leftplusrightllc/canvas-lms,Rvor/canvas-lms,Unow/canvas-lms,HotChalk/canvas-lms,sdeleon28/canvas-lms,ShreniiNepal/shrenii_lmp,AndranikMarkosyan/lms,roxolan/canvas-lms,whalejasmine/canvas-lms,va7map/canvas-lms,shidao-fm/canvas-lms,ShreniiNepal/shrenii_lmp,sdeleon28/canvas-lms,wrdsb/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,wrdsb/canvas-lms,sfu/canvas-lms,dgynn/canvas-lms,Unow/canvas-lms,venturehive/canvas-lms,AndranikMarkosyan/lms,shidao-fm/canvas-lms,matematikk-mooc/canvas-lms,grahamb/canvas-lms,fronteerio/canvas-lms,instructure/canvas-lms,leftplusrightllc/canvas-lms,sfu/canvas-lms,antoniuslin/canvas-lms,venturehive/canvas-lms,roxolan/canvas-lms,snehakachroo1/LSI_replica,gbleydon/canvas-lms,narigone/canvas,jay3126/canvas-lms,antoniuslin/canvas-lms,dgynn/canvas-lms,narigone/canvas,redconfetti/canvas-lms,sfu/canvas-lms,HotChalk/canvas-lms,efrj/canvas-lms,grahamb/canvas-lms,wrdsb/canvas-lms,venturehive/canvas-lms,tgroshon/canvas-lms,matematikk-mooc/canvas-lms,instructure/canvas-lms,utkarshx/canvas-lms,narigone/canvas,instructure/canvas-lms,whalejasmine/canvas-lms,jay3126/canvas-lms,samuels410/greatlakes-lms,leftplusrightllc/canvas-lms,juoni/canvas-lms,kyroskoh/canvas-lms,redconfetti/canvas-lms,kyroskoh/canvas-lms,samuels410/greatlakes-lms,juoni/canvas-lms,grahamb/canvas-lms,Rvor/canvas-lms,tgroshon/canvas-lms,ShreniiNepal/shrenii_lmp,djbender/canvas-lms,matematikk-mooc/canvas-lms,sfu/canvas-lms,greyhwndz/canvas-lms,kyroskoh/canvas-lms,snehakachroo1/LSI_replica,redconfetti/canvas-lms,fronteerio/canvas-lms,SwinburneOnline/canvas-lms,djbender/canvas-lms,tgroshon/canvas-lms,dgynn/canvas-lms,gbleydon/canvas-lms,efrj/canvas-lms,Jyaasa/canvas-lms,gbleydon/canvas-lms,matematikk-mooc/canvas-lms,fronteerio/canvas-lms,tgroshon/canvas-lms,jay3126/canvas-lms,va7map/canvas-lms,sdeleon28/canvas-lms,roxolan/canvas-lms,kyroskoh/canvas-lms,HotChalk/canvas-lms,instructure/canvas-lms,va7map/canvas-lms,Rvor/canvas-lms,Jyaasa/canvas-lms,wye0220/shindig-canvas,shidao-fm/canvas-lms,grahamb/canvas-lms,shidao-fm/canvas-lms,instructure/canvas-lms,samuels410/greatlakes-lms,juoni/canvas-lms,eCNAP/CANVAS,greyhwndz/canvas-lms,antoniuslin/canvas-lms,antoniuslin/canvas-lms,samuels410/greatlakes-lms,eCNAP/CANVAS,dgynn/canvas-lms,AndranikMarkosyan/lms,SwinburneOnline/canvas-lms,ShreniiNepal/shrenii_lmp