Feature request: ability to use non-"local" policy_group when exporting policies

When running integration tests via TestKitchen, it would be useful to test behavior dependent on the value of policy_group. However, chef export hardcodes the value of policy_group to local:

      # Policy groups provide namespaces for policies so that a Chef Server can
      # have multiple active iterations of a policy at once, but we don't need
      # this when serving a single exported policy via Chef Zero, so hardcode
      # it to a "well known" value:
      POLICY_GROUP = 'local'.freeze

This is a proposal for a feature that would allow setting the value of policy_group via a per-suite setting in .kitchen.yml. On the ChefDK side, this would require making POLICY_GROUP a configurable option to chef export.

Start with the chef export implementation in lib/chef-dk/policyfile_services/export_repo.rb, especially the POLICY_GROUP constant, and review the linked Test Kitchen issue for the integration-test context. Trace how a per-suite setting in .kitchen.yml could reach chef export; done means policy_group is configurable rather than always local and the requested Test Kitchen behavior can be tested.