This refactors the docs publication/promote jobs so that there
are base versions which can be consumed by tenants who will supply
their own AFS secrets, as well as versions for use in this tenant
(which consume the base versions in exactly the way another tenant
would).
The documentation policies for the tenant are encoded in the secret,
so each tenant can choose the publication locations and scheme once
and allow all projects within that tenant to use these jobs.
Change-Id: I8f201c0351d4d532ddcbcf1f22f9297dece04fff
edab04d5ef