* Add Yubikey PrivateKey implementation for use by Teleport clients.
- Add yubikey login logic, reusing previously stored private keys.
- Fix identity file decoding with PIV keys, which sign ecdsa certificates.
- Add libpcsclite-dev pre-req for building on linux.
- Remove unnecessary keys.Signer interface and move its functionality to keys.PrivateKey.
- Move retry and jitter utils to new api/utils/retryutils package.