feat: add option to keep payload fields when creating JWT VC/VP

[mirceanis]

During JSON <-> JWT transformation the fields that are mentioned in the vc-data-model encoding are removed by default.

This PR adds the option to keep the JSON fields in the JWT payload when creating verifiable credentials & presentations.

To keep the respective fields (effectively duplicating the data they contain) one can set the removeOriginalFields option to false:

Examples:

const verifiableCredential = await agent.createVerifiableCredential({
  credential: {
    issuer: { id: identifier.did },
    credentialSubject: {
      id: 'did:web:example.com',
      you: 'Rock',
    },
  },
  proofFormat: 'jwt',
  removeOriginalFields: false,
})

const verifiablePresentation = await agent.createVerifiablePresentation({
  presentation: {
    // ...
  },
  proofFormat: 'jwt',
  removeOriginalFields: false,
})

fixes #394

[codecov]

Codecov Report

Merging #431 (8214247) into next (0bf7b24) will decrease coverage by 1.78%.
The diff coverage is 64.35%.

❗ Current head 8214247 differs from pull request most recent head bc471e2. Consider uploading reports for the commit bc471e2 to get more accurate results

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