message: Add NamedChain for pre-mainnet
  We should be able to start using a stable chain ID for pre-mainnet, add
  a named chain.
  Closes:
diff: @@ -24,6 +24,7 @@ pub enum NamedChain {
  TESTNET = 2,
  DEVNET = 3,
  TESTING = 4,
  + PREMAINNET = 5,
  }
  impl NamedChain {
  @@ -34,6 +35,7 @@ impl NamedChain {
  "TESTNET" => NamedChain::TESTNET,
  "DEVNET" => NamedChain::DEVNET,
  "TESTING" => NamedChain::TESTING,
  + "PREMAINNET" => NamedChain::PREMAINNET,
  _ => {
  return Err(format_err!("Not a reserved chain: {:?}", s));
  }
  @@ -51,6 +53,7 @@ impl NamedChain {
  2 => Ok(NamedChain::TESTNET),
  3 => Ok(NamedChain::DEVNET),
  4 => Ok(NamedChain::TESTING),
  + 5 => Ok(NamedChain::PREMAINNET),
  _ => Err(String::from("Not a named chain")),
  }
  }
  @@ -123,6 +126,7 @@ impl Display for NamedChain {
  NamedChain::TESTNET => "TESTNET",
  NamedChain::MAINNET => "MAINNET",
  NamedChain::TESTING => "TESTING",
  + NamedChain::PREMAINNET => "PREMAINNET",
  }
  )
  }
  