Add LndHub.go module

* Accounting wrapper for the Lightning Network aka L3
* only LND is supported atm, CLN is planned
* packaged in nixpkgs: https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/blockchains/lndhub-go/default.nix
* requires `lnd` and `postgresql`
* upstream: https://github.com/getAlby/lndhub.go