Add JiHu project templates dir

What does this MR do and why?

Closes #901 (closed), use override to add JiHu-only project template dir.

How to set up and validate locally

1. Add a template into localized_jh_templates_table method of jh/spec/lib/jh/gitlab/project_template_spec.rb, like:

   ::Gitlab::ProjectTemplate.new('jihu-only', 'jihu-only', _('jihu-only'), 'jihu-only', 'jihu-only')

2. Get the test result in Rails Console(JiHu environment):

   Gitlab::ProjectTemplate.find('jihu-only').archive_path

3. You will see that the test result cantains jh/vendor/project_templates