Add support for core lightning watchtower TEoS (The Eye of Satoshi) - server and client

[seberm]

This MR adds basic support for rust-teos - package, module and clightning watchtower plugin.

Fixes: #540

TODO(s):

• GPG-sign releases/tags or commits talaia-labs/rust-teos#116
• "Too many open files" error when running teos tests talaia-labs/rust-teos#119
• Add teos package (The Eye of Satoshi) with clightning watchtower plugin NixOS/nixpkgs#195782
• Update nixpgks #560

[HaosGames]

Looks good to me.
I started testing this now with CLN as a backend and the teos daemon on a separate host with a pruned bitcoind.
Works great so far with minimal configuration.

[HaosGames]

Still running great on my side. I would love to see this in a release.

[sr-gi]

I'm planning to cut a release sooner rather than later, which will include all the changes pointed out in the PR description AFAICT. Is there anything else that'd needed?

[JosephGoulden]

I'm running the watchtower and plugin modules from this PR and its working well.

It would be nice to have a service that automatically registers with the tower and renews the subscription when needed. But we can add that later.

Also I opened a PR to add a flake to TEOS.

[seberm]

@nixbitcoin @erikarvstedt @jonasnick

Is it worthwhile to continue working on and rebasing this PR? Is there a possibility that nix-bitcoin will incorporate these changes?
Thanks!