Make Gitlab::GlRepository#types an instance method

Having this as an instance method makes it easier to override in the
prepended `EE` module.

If we try to override this method on the module itself, it would not
be overridden correctly, depending on the load order.

lib/gitlab/gl_repository.rb

 # frozen_string_literal: true
 
 module Gitlab
-  module GlRepository
+  class GlRepository
+    include Singleton
+
     PROJECT = RepoType.new(
       name: :project,
       access_checker_class: Gitlab::GitAccess,
@@ -19,7 +21,7 @@ module Gitlab
     }.freeze
 
     def self.types
-      TYPES
+      instance.types
     end
 
     def self.parse(gl_repository)
@@ -39,5 +41,11 @@ module Gitlab
     def self.default_type
       PROJECT
     end
+
+    def types
+      TYPES
+    end
+
+    private_class_method :instance
   end
 end

lib/gitlab/gl_repository/repo_type.rb

 # frozen_string_literal: true
 
 module Gitlab
-  module GlRepository
+  class GlRepository
     class RepoType
       attr_reader :name,
                   :access_checker_class,