Add the ability to join networks to "seed mode" so that we can run a seed cluster

[bhechinger]

To be able to reasonably run this in kubernetes we need to be able to run multiple seed pods.

This change has nodes run in p2p-beacon mode to try to join an existing network. This allows us two things.

• Running a seed cluster where there are multiple seed nodes
• Completely shut down the seed nodes being able to start them back up by bootstrapping off an existing network

At start the seed will attempt to contact the nodes listed in the discovery list. After enough attempts instead of failing it will fall back to bootstrapping a brand new network.

[bhechinger]

I think there are some modifications that came from my branch that I merge yesterday. Perhaps you'll need to rebase from main?

I had already re-based but it mangled the formatting. I just needed to re-run cargo fmt

[bhechinger]

I'm fine with the PR in general, but maybe Nix files could be extracted into separate PR and checked for dependencies?

Oh shoot, I missed this message before merging. Let's catch up on slack about how to handle this.