feat(jans-cedarling): in sidecar, move tokens to subject

[SafinWasi]

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Description

As per discussion, the token(s) passed to the sidecar will be expected to be in the subject field of the payload as per AuthZen specs. An example of this:

{
    "subject": {
        "type": "JWT",
        "id": "cedarling",
        "properties": {
            "access_token": "..."
       }
    }
}

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Prepare

• Read contribution guidelines
• Read license information

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Identified code changes

• Refactor the cedarling module to parse tokens from subject instead of context

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Test cases and code coverage

• Start adding test cases and coverage

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Document the changes

• Update documentation example