Create a CLI argument to set up the Discovery and Connetion initiation Lookup Rate

We have that Interval [hardcoded](https://github.com/lambdaclass/ethrex/blob/main/crates/networking/p2p/discv4/server.rs#L42-L43), and it can be useful to be able to parametrize it in the command line to test different configurations. Let's create a CLI arg for it