Align codebase with openshift/cincinnati (prepare for folding back there)

[lucab]

Once the development dust settles here, this project should be folded back into https://github.com/openshift/cincinnati.

A list of things that need to happen before being able to do that:

• split into two binaries, fcos-graph-builder and fcos-policy-engine
• decommission dumnati binary
• rework graph-processing logic into plugins

[lucab]

Ratcheting changes here, I think a good first step would be introducing fcos-graph-builder binary first and capturing the shared logic in a commons library.
That can be deployed to fedora-infra in order to check that everything is fine, without impacting clients.

Once there, the next thing is landing fcos-policy-engine and routing request to it instead of dumnati. This is the most sensitive step as it impacts clients, so we should keep that in mind and make it easy to switch (perhaps running all the three components for some time and just switching the endpoint service in openshift).

After that, if all goes well, we can remove the dumnati crate.