Create workflow for versioned releases

[bertday]

It would be good to come up with a process for releasing AIS updates under unique versions. This will ensure that existing users are supported without holding up development of new features and breaking changes. Some good guidelines for versioning can be found in the semver specification.

Part of this project will be coming up with a clear, intuitive definition for what qualifies as a breaking change. Such as:

A breaking change is anything that changes or removes fields names or field types in the API response

There are a few considerations:

• How would new versions get reflected Gatekeeper? (We would only need separate entries for each major version.)
• What's the cost of hosting multiple major versions on Elastic Beanstalk?
• What's the process for deprecating older versions and helping users upgrade their code?

Also, part of the process should be bumping the version in setup.py.