feat: new "at_policy" package for building policy services on atProtocol

[gkc]

- What I did

• new package at_policy
• added at_policy to the build / test matrix in .github workflows
• added core unit tests

The at_policy library provides generic scaffolding for

• building policy management services
• with which policy enforcement endpoints communicate via atProtocol
• using the atClient libraries
• and therefore get all the benefits of using atProtocol and the atClient libraries - outbound communication only, end-to-end encryption, using atSigns rather than IP addresses, etc

- How I did it

• Added core code
• Added tests
• Added main README
• Added examples and a README in the examples directory

- How to verify it
Tests pass

[cpswan]

What's the plan to add this to the automated tests we run from at_libraries/.github/workflows/at_libraries.yaml?

[gkc]

What's the plan to add this to the automated tests we run from at_libraries/.github/workflows/at_libraries.yaml?

Already done

[gkc]

@XavierChanth just noticed that I hadn't updated example/bin/service.dart to use PolicyService, which I added after the initial implementation in order to simplify the policy service development experience ... I'll update this tomorrow morning, maybe this evening although unlikely

[gkc]

@XavierChanth just noticed that I hadn't updated example/bin/service.dart to use PolicyService, which I added after the initial implementation in order to simplify the policy service development experience ... I'll update this tomorrow morning, maybe this evening although unlikely

Actually that's incorrect - policy.dart is using PolicyService - service.dart is not because it is the service which is calling the policy service. In a version 1.1 I may add a PolicyClient to make it easier to write clients of the policy service