Add a --bootnodes flag for reth node

[onbjerg]

Describe the feature

Currently we always use mainnet bootnodes, but they should be resolved loading the bootnodes chainspec (should be handled in #485). We should also provide the ability to override the bootnodes by specifying a --bootnodes flag.

The format should be --bootnodes <enrs> where <enrs> is a comma-seperated list of Ethereum node records.

The type should be Option<Vec<NodeRecord>>.

Additional context

To parse comma-separated values, clap provides value_delimiter. Example:

struct Opts {
  #[arg(long, value_delimiter = ',')]
  nodes: Option<Vec<NodeRecord>>
}

[literallymarvellous]

I'd 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 😄