Add a --nat flag to reth node

[onbjerg]

Describe the feature

It should be possible to specify what kind of NAT mechanism to use when invoking reth node.

The supported methods can be found here:

reth/crates/net/nat/src/lib.rs

Line 25 in e6ca4c5

pub enum NatResolver {

The flag should be: --nat <method>, where <method> is any of:

• any
• upnp
• auto (maps to PublicIp)
• extip:<ip> (maps to ExternalIp)
• none (maps to None)

The default should be any.

Ideally, the NatResolver enum would be re-used for the CLI to not duplicate code.

The resolution method is set on NetworkConfigBuilder using:

builder::discovery(
  Discv4Config::builder()
    .external_ip_resolver(Some(nat_resolution_method))
)

Additional context

No response

[literallymarvellous]

Would like to take this

[onbjerg]

Thanks! I've assigned you to the issue. If you feel stuck, open up a draft PR with your questions and someone will help you. If you are prevented from solving the issue, let me know and I will unassign you 😄