Define a clear format for ACI policy specification

[DomAyre]

Why

As part of Azure#9167 and our ambition to have more modular steps in the policy generation process, it makes sense to have a simple, well defined spec for the JSON which describes the policy to be generated.

I have opted to go with python data classes to define this, it's a python first approach which keeps the code simple, and also allow us to generate docs, json schemas from a single source of truth.

How

• Define a series of data classes, rooted in AciPolicySpec which specifies the format of the json which we use to generate the policy
• Add a couple of example parsers including one for ARM templates
• Update load_policy_from_arm_template_str() to use this parser
• Since instances of AciPolicySpec are complete including fields which were previously implicitly added at policy gen time, add some code to avoid duplication of these implicit fields.
• Update interface of load_policy_from_arm_template_file()
  • The field fragment_contents is never given in the codebase so it is removed, and rego_imports is renamed to included_fragments
• Checked all existing use cases, and ensured they are still supported

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This checklist is used to make sure that common guidelines for a pull request are followed.

Related command

General Guidelines

• Have you run azdev style <YOUR_EXT> locally? (pip install azdev required)
• Have you run python scripts/ci/test_index.py -q locally? (pip install wheel==0.30.0 required)
• My extension version conforms to the Extension version schema

NOTE: Version is currently already bumped by #4 but if that's released before this, we need to bump the version again

[github-actions]

Hi @DomAyre

Release Suggestions

Module: confcom

• Please log updates into to src/confcom/HISTORY.rst
• Update VERSION to 1.2.9 in src/confcom/setup.py

Notes

• For more info about extension versioning, please refer to Extension version schema

[DomAyre]

Moved to Azure#9262