Add nonce field in JWT.Claims()

[EbonyLouis]

Reason

In our Known Customer Credential Wallet guide we need to be able to include the cNonce in the claims to then be signed and sent over to the issuer

Goal:

 let jwtClaims = JWT.Claims(
        issuer: userBearerDid.uri, // user's DID string
        audience: issuerBearerDid.uri, // Issuer's DID string
        issuedAt: issuedAtDate,
        nonce: cNonce
    )

 let signedJwt = try JWT.sign(did: userBearerDid, claims: jwtClaims)