Create some sort of guidelines / linter to this project

[Gerrit91]

There are quite some implicit conventions used in our Ansible repositories and they are trying to serve a good purpose:

• They are targeted to reduce breaking changes for the deployment, which are extremely hard to trace down for adopters.
• They are aiming towards high versatility to make the deployment fit for very different environments.

As it's often pretty hard to forget something or violate the conventions as a developer, we should try to at least write them up or even better write a CI linter which enforces the rules.