graphql: add muted attribute to assignments

closes RECNVS-408

Test plan:
  query assignment muted status with graphql

Change-Id: Ia29d34f4652ddc6a93851a3fa7a1fd88d7af144e
Reviewed-on: https://gerrit.instructure.com/145935
Reviewed-by: Michael Jasper <mjasper@instructure.com>
Tested-by: Jenkins
QA-Review: Collin Parrish <cparrish@instructure.com>
Product-Review: Cameron Matheson <cameron@instructure.com>

app/graphql/types/assignment_type.rb

@@ -40,6 +40,8 @@ module Types
       "when this assignment is due",
       property: :due_at
 
+    field :muted, types.Boolean, property: :muted?
+
     field :state, !AssignmentState, property: :workflow_state
 
     field :assignmentGroup, AssignmentGroupType, resolve: ->(assignment, _, _) {

schema.graphql

@@ -30,6 +30,7 @@ type Assignment implements Node, Timestamped {
   gradingType: GradingType
   htmlUrl: URL
   id: ID!
+  muted: Boolean
   name: String
   needsGradingCount: Int
 

spec/graphql/types/assignment_type_spec.rb

@@ -58,6 +58,7 @@ describe Types::AssignmentType do
     expect(assignment_type.state).to eq assignment.workflow_state
     expect(assignment_type.onlyVisibleToOverrides).to eq assignment.only_visible_to_overrides
     expect(assignment_type.assignmentGroup).to eq assignment.assignment_group
+    expect(assignment_type.muted).to eq assignment.muted?
   end
 
   describe "submissionsConnection" do