feat(mono): relative path + cli configuration for multiple L2s

[CeciliaZ030]

These are now configurable:

pub struct L2Args {
    #[arg(long = "l2.chain_ids", required = true, num_args = 1..,)]
    pub chain_ids: Vec<u64>,

    #[arg(long = "l2.datadirs", required = true, num_args = 1..,)]
    pub datadirs: Vec<PathBuf>,

    #[arg(long = "l2.ports", num_args = 1..,)]
    pub ports: Vec<u16>,

    #[arg(long = "l2.ipc_path")]
    pub ipc_path: String,
}

When you run L2 with reth node --l2.chain_ids <blah blah> --l2.datadirs <blah blah>, these two are mandatory. Ports and IPC can be default. These's only one ipc_path cuz it's a column shared btw Reth, inside we have specific ipc files:

Also Reth data volumes are shared per L2: