add body to submission draft mutation in graphql

we need to allow setting a 'body' in the submission draft
mutation in graphql for text entry assignments

Test Plan:
* create an assignment as a teacher
* add a student to that assignment
* as a student, navigate to /graphiql
* run the following mutation
** set the submissionId to whatever your latest submissionId is
```
mutation {
  createSubmissionDraft(input: {submissionId: "1", attempt: 1, body: "stuff"}) {
    errors {
      message
      attribute
    }
    submissionDraft {
      _id
      body
    }
  }
}
```

* you should get a result like:
```
{
  "data": {
    "createSubmissionDraft": {
      "errors": null,
      "submissionDraft": {
        "_id": "42"
        "body": "stuff",
      }
    }
  }
}
```

* in the rails console, confirm the data (especially the body)
  is correct: SubmissionDraft.find(<id>)

fixes COMMS-2265

Change-Id: I6ba6a67e3a592e295c62365ca7fa13250d05e837
Reviewed-on: https://gerrit.instructure.com/203731
QA-Review: Matthew Lemon <mlemon@instructure.com>
Reviewed-by: Matthew Lemon <mlemon@instructure.com>
Tested-by: Jenkins
Product-Review: Ryan Norton <rnorton@instructure.com>

app/graphql/mutations/create_submission_draft.rb

@@ -29,12 +29,14 @@ class Mutations::CreateSubmissionDraft < Mutations::BaseMutation
   # create the `SubmissionDraft` for an old attempt and not return it back in
   # subsequent graphql queries for submission drafts.
   argument :attempt, Integer, required: false
+  argument :body, String, required: false
   argument :file_ids, [ID], required: false, prepare: GraphQLHelpers.relay_or_legacy_ids_prepare_func('Attachment')
   argument :submission_id, ID, required: true, prepare: GraphQLHelpers.relay_or_legacy_id_prepare_func('Submission')
 
   field :submission_draft, Types::SubmissionDraftType, null: true
   def resolve(input:)
     submission = find_submission(input[:submission_id])
+
     file_ids = (input[:file_ids] || []).compact.uniq
     attachments = get_and_verify_attachments!(file_ids)
     verify_allowed_extensions!(submission.assignment, attachments)
@@ -44,6 +46,10 @@ class Mutations::CreateSubmissionDraft < Mutations::BaseMutation
       submission_attempt: input[:attempt] || (submission.attempt + 1)
     ).first_or_create!
     submission_draft.attachments = attachments
+    # for drafts we allow the body to be null or empty, so there's nothing to validate
+    submission_draft.body = input[:body]
+    submission_draft.save!
+
     {submission_draft: submission_draft}
   rescue ActiveRecord::RecordNotFound
     raise GraphQL::ExecutionError, 'not found'

schema.graphql

@@ -1005,6 +1005,7 @@ Autogenerated input type of CreateSubmissionDraft
 """
 input CreateSubmissionDraftInput {
   attempt: Int
+  body: String
   fileIds: [ID!]
   submissionId: ID!
 }

spec/graphql/mutations/create_submission_draft_spec.rb

@@ -31,6 +31,7 @@ RSpec.describe Mutations::CreateSubmissionDraft do
   def mutation_str(
     submission_id: @submission.id,
     attempt: nil,
+    body: nil,
     file_ids: []
   )
     <<~GQL
@@ -38,6 +39,7 @@ RSpec.describe Mutations::CreateSubmissionDraft do
         createSubmissionDraft(input: {
           submissionId: "#{submission_id}"
           #{"attempt: #{attempt}" if attempt}
+          #{"body: \"#{body}\"" if body}
           fileIds: #{file_ids}
         }) {
           submissionDraft {
@@ -47,6 +49,7 @@ RSpec.describe Mutations::CreateSubmissionDraft do
               _id
               displayName
             }
+            body
           }
           errors {
             attribute
@@ -58,7 +61,7 @@ RSpec.describe Mutations::CreateSubmissionDraft do
   end
 
   def run_mutation(opts = {}, current_user = @student)
-    result = CanvasSchema.execute(mutation_str(opts), context: {current_user: current_user})
+    result = CanvasSchema.execute(mutation_str(opts), context: {current_user: current_user, request: ActionDispatch::TestRequest.create})
     result.to_h.with_indifferent_access
   end
 
@@ -99,6 +102,17 @@ RSpec.describe Mutations::CreateSubmissionDraft do
     ).to eq second_result.dig(:data, :createSubmissionDraft, :submissionDraft, :submissionAttempt)
   end
 
+  it 'allows you to set a body on the submission draft' do
+    result = run_mutation(
+      submission_id: @submission.id,
+      attempt: @submission.attempt,
+      body: 'some text body'
+    )
+    expect(
+      result.dig(:data, :createSubmissionDraft, :submissionDraft, :body)
+    ).to eq 'some text body'
+  end
+
   it 'returns an error if the attachments are not owned by the user' do
     attachment = attachment_with_context(@teacher)
     result = run_mutation(
@@ -145,7 +159,7 @@ RSpec.describe Mutations::CreateSubmissionDraft do
     ).to eq 'submission draft cannot be more then one attempt ahead of the current submission'
   end
 
-  it "uses the submission attempt plus one if an explicit attempt isn't provided" do
+  it 'uses the submission attempt plus one if an explicit attempt is not provided' do
     result = run_mutation(
       submission_id: @submission.id,
       file_ids: [@attachments[0].id]