Decrypt pillar data through the builtin GPG renderer

In most cases, you'll want to make this the last external pillar used. For example, to pair with the builtin stack pillar you could do something like this:

  - stack: /path/to/stack.cfg
  - gpg: {}

Set gpg_keydir in your config to adjust the homedir the renderer uses.

salt.pillar.gpg.ext_pillar(minion_id, pillar, *args, **kwargs)