[Feature Request] Define common models like JSON Web Key (JWK)

**Is your feature request related to a problem? Please describe.**
The REST API Stewardship Board has seen a number of services use JWKs or their variants e.g., JWTs, and related times like JWEs as part of JOSE declarations e.g., https://github.com/Azure/azure-rest-api-specs-pr/issues/16580#issuecomment-1919601365

**Describe the solution you'd like**
We should define these standard types and allow them to be imported. That might also help us with client generation where having a specific type we know about might lend itself in some languages e.g., .NET to use built-in support. At the very least, it helps ensure that every service using JWKs are defining them correctly and consistently.

**Describe alternatives you've considered**
It could even be in a separate library instead of Foundation or Core (I doubt ARM would need it).

No files, tests, or entry points are named. Review how shared models are defined and imported from Foundation or Core, then determine whether JWK, JWT, and JWE belong there or in a separate library; done means the chosen standard types are consistently defined and importable for REST API use.

Written by the indexing model from the issue text.