Configure CI to build AMI automatically on a new tag

Goal

Configure CI to build AMI automatically and get rid of manual build/deploy steps for AWS.

TODO / How to implement

• add CI rules to run Marketplace jobs (use a new prefix cf/, for example cf/3.1.2)
• define jobs to build AMI and generate Cloud Formation templates
• prepare release candidate (cf/3.1.2-rc.0) jobs to test before a Marketplace review and final release (cf/3.1.2) jobs

Acceptance criteria