feat: support string parameters in permits

[stonelgh]

To support string paramters and string literal arguments in permits definition

Related issue(s)

#1113

Checklist

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• I have referenced an issue containing the design document if my change
  introduces a new feature.
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• I have added tests that prove my fix is effective or that my feature
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Further Comments

[CLAassistant]

All committers have signed the CLA.

[zepatrik]

Hey, thanks for putting all of this work in!
We have to consider the impacts of this for all planned and upcoming features though, as it might interfere with those. Because that is non-trivial, it might take some time. We have already thought about a similar feature btw: #319 (comment)

[stonelgh]

Got that. Let me know if you need assistance.

[TomOperator]

@stonelgh I was attempting to build similar logic (GCP-style IAM) and immediately realised this is essential to decouple objects from their relations to subjects (white flag). @zepatrik this would be a significant enhancement to the specification - do we see this landing in the near future?