message: Set retry token secret in ProxygenQuicServer
  Summary:
  Created a secret in keychain called QUIC_RETRY_TOKEN_SECRET (https://fburl.com/hipster/cjwmt0bu), which will be used for encrypting / decrypting retry tokens
  Since mvfst is open source, retrieve and set this secret in ProxygenQuicServer
diff: @@ -210,6 +210,9 @@ struct TransportSettings {
  // default stateless reset secret for stateless reset token
  folly::Optional<std::array<uint8_t, kStatelessResetTokenSecretLength>>
  statelessResetTokenSecret;
  + // retry token secret used for encryption/decryption
  + folly::Optional<std::array<uint8_t, kRetryTokenSecretLength>>
  + retryTokenSecret;
  // Default initial RTT
  std::chrono::microseconds initialRtt{kDefaultInitialRtt};
  // The active_connection_id_limit that is sent to the peer.
  