feat: expose function to generate OPL

[hperl]

With the OPL landed, we want to expose some functionality to migrate from the legacy namespaces to the OPL-defined namespaces.

This PR exposes a GenerateOPLConfig function to do this. Exposing this in the Keto CLI is future work.

Related issue(s)

Checklist

• I have read the contributing guidelines.
• 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

[zepatrik]

Nice, I like the idea 😜