Publish gathered facts using contract

[arbulu89]

First interaction with the contracts repository to publish the gathered facts.

Basically, it uses the contracts project to build the answer.

I have introduced the policy.go file to make it as similar as the wanda side (followed the old PR: #73). The facts gathering request logic will go in this file as well.

Some next step:

• Create a entities package within the factsengine to store the used structs (now in facts.go). We need to align the structs there with the ones defined in the contracts, following similar naming convention, fields, etc
• Unify naming conventions and rabbitmq usage values, like exchange names, queues, etc
• Do the same operation with the facts gathering request message, which is consumed by the agent. Pending to define the format of this message yet.

[CDimonaco]

LGTM