Periodically release collection

[dometto]

To make it easier to use this collection in other repositories it would help to have some kind of versioning in place. We don't want to have to think in terms of release milestones, I think, so one idea is:

• track the collection version here
• whenever you make a change that is not backwards compatible (e.g. deleting a role, or adding a required parameter from a playbook), bump the major version number
• periodically, e.g. once per month:
  • retag the major version (v1) -- this ensures that repositories requiring v1 get the latest version.
  • tag with the major version (v1.1) -- this ensures that you can require e.g. v1.1 exactly.

This allows other repositories to depend on more or less stable versions of this collection, without having to depend on a specific commit (and thus not get bugfixes/patches).

Eventually, we could also publish the collection on Ansible Galaxy, but this is not required.