Add IssuableSortEnum and IssueSortEnum

this lays the basis for in progress MRs

app/graphql/resolvers/issues_resolver.rb

@@ -35,7 +35,7 @@ module Resolvers
               description: 'Issues closed after this date'
     argument :search, GraphQL::STRING_TYPE, # rubocop:disable Graphql/Descriptions
               required: false
-    argument :sort, Types::SortEnum,
+    argument :sort, Types::IssueSortEnum,
               description: 'Sort issues by this criteria',
               required: false,
               default_value: 'created_desc'

app/graphql/types/issuable_sort_enum.rb

+# frozen_string_literal: true
+
+module Types
+  # rubocop: disable Graphql/AuthorizeTypes
+  class IssuableSortEnum < SortEnum
+    graphql_name 'IssuableSort'
+    description 'Values for sorting issuables'
+  end
+  # rubocop: enable Graphql/AuthorizeTypes
+end

app/graphql/types/issue_sort_enum.rb

+# frozen_string_literal: true
+
+module Types
+  # rubocop: disable Graphql/AuthorizeTypes
+  class IssueSortEnum < IssuableSortEnum
+    graphql_name 'IssueSort'
+    description 'Values for sorting issues'
+  end
+  # rubocop: enable Graphql/AuthorizeTypes
+end