Add UserCallout GraphQL type

Creates the UserCallout GraphQL type

app/graphql/types/user_callout_feature_name_enum.rb

+# frozen_string_literal: true
+
+module Types
+  class UserCalloutFeatureNameEnum < BaseEnum
+    graphql_name 'UserCalloutFeatureNameEnum'
+    description 'Name of the feature that the callout is for'
+
+    ::UserCallout.feature_names.keys.each do |feature_name|
+      value feature_name.upcase, value: feature_name
+    end
+  end
+end

app/graphql/types/user_callout_type.rb

+# frozen_string_literal: true
+
+module Types
+  # rubocop:disable Graphql/AuthorizeTypes
+  class UserCalloutType < BaseObject
+    graphql_name 'UserCallout'
+
+    field :feature_name, UserCalloutFeatureNameEnum, null: false,
+      description: 'Name of the feature that the callout is for.'
+    field :dismissed_at, Types::TimeType, null: true,
+      description: 'Date when the callout was dismissed.'
+  end
+  # rubocop:enable Graphql/AuthorizeTypes
+end

spec/graphql/types/user_callout_feature_name_enum_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe GitlabSchema.types['UserCalloutFeatureNameEnum'] do
+  specify { expect(described_class.graphql_name).to eq('UserCalloutFeatureNameEnum') }
+
+  it 'exposes all the existing user callout feature names' do
+    expect(described_class.values.keys).to match_array(::UserCallout.feature_names.keys.map(&:upcase))
+  end
+end

spec/graphql/types/user_callout_type_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe GitlabSchema.types['UserCallout'] do
+  specify { expect(described_class.graphql_name).to eq('UserCallout') }
+
+  it 'has expected fields' do
+    expect(described_class).to have_graphql_fields(:feature_name, :dismissed_at)
+  end
+end