Fixes n+1 on submissionComments query
Fixes n+1 on submissionComments query

closes VICE-2240

flag=none

test plan:
  - Specs pass
  - See logs to verify that N+1 isn't happening by
      running this query on graphiql:
      query MyQuery {
        legacyNode(_id: "6", type: User) {
          ... on User {
            submissionCommentsConnection {
              nodes {
                _id
                comment
              }
            }
          }
        }
      }

qa risk: low

Change-Id: I67b4bec87d3e80a2bbb6b90cb4f62ea6703c98b7
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/278179
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>
QA-Review: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>
Product-Review: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>

instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms