Free certificates unit's init state for includes

Summary:
Plan is to deploy Let's Encrypt a unified way through
the certificates unit too. As such, init.sls will be
used for includes.

Ref T1505.

Reviewers: DorianWinty

Reviewed By: DorianWinty

Maniphest Tasks: T1505

Differential Revision: https://devcentral.nasqueron.org/D3247