Add ability to encode a token using a secret key about jwt-cli

[alexanderankin]

btw we can now do things like:

npx alexanderankin/jwt-cli#encoding encode --header.alg RS256 --verbose

and it will produce:

$ npx alexanderankin/jwt-cli#encoding encode --header.alg RS256 --verbose --body.sub john --body.scopes "openid read.profile"
{
  "message": "printing generated key because verbose mode is selected",
  "secret": "-----BEGIN RSA PRIVATE KEY-----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\nkOUNQ1f5tafq19RWidQp2kzhr1C7rrFm/AHv8uT3T2M=\n-----END RSA PRIVATE KEY-----\n",
  "generatedPublicKey": "-----BEGIN RSA PUBLIC KEY-----\nMIGJAoGBALBHunIxq2pVG7uDDJ0FMy/myHZgS5e3ezN3b+Qu/QOkcGbWAfqIfUVq\nPObqmQzskTLUNdMksbDzVfjGNg+0aziqoEyh2v7uoY20trPg7yWT6T831PxR3smg\nDlaGTOfupr6LIJrxMmA3Rcob08uJIdrWahXTjZvm/uC0OGyjEqQRAgMBAAE=\n-----END RSA PUBLIC KEY-----\n"
}
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