feat: add holochain nixos module, nix extra-container package with test

[steveej]

this introduces a nixos module for holochain, an extra-container package
with the (almost) default config, and a VM test to ensure the
admin-websocket becomes available on the host.

---

closes https://github.com/Holo-Host/holo-host-private/issues/100

• integration test that demonstrates the admin websocket becomes ready

[root@towards-allograph:~]# /nix/store/7kglpki3ls5f41s0ldgqb8p2v3cyx6qh-container/bin/container create
[root@towards-allograph:~]# /nix/store/7kglpki3ls5f41s0ldgqb8p2v3cyx6qh-container/bin/container start holochain
[root@towards-allograph:~]# machinectl shell holochain /bin/sh -c "PAGER='' systemctl status holochain"
Connected to machine holochain. Press ^] three times within 1s to exit session.
● holochain.service
     Loaded: loaded (/etc/systemd/system/holochain.service; enabled; preset: ignored)
     Active: active (running) since Tue 2025-02-18 20:35:22 UTC; 1min 4s ago
 Invocation: b6647b92dfe54f90878bcbc080131e7f
    Process: 298 ExecStartPre=/nix/store/i8b3wl9vnn1cfm8ij9mkihn2p29ibkpv-unit-script-holochain-pre-start/bin/holochain-pre-start (code=exited, status=0/SUCCESS)
   Main PID: 312 (holochain-start)
         IO: 0B read, 424K written
      Tasks: 26 (limit: 19061)
     Memory: 10.1M (peak: 266.8M)
        CPU: 2.260s
     CGroup: /system.slice/holochain.service
             ├─312 /nix/store/gwgqdl0242ymlikq9s9s62gkp5cvyal3-bash-5.2p37/bin/bash /nix/store/mb0inbiq9hdc0fjdfxird0kxk8l5jwr4-unit-script-holochain-start/b…
             ├─315 /nix/store/gwgqdl0242ymlikq9s9s62gkp5cvyal3-bash-5.2p37/bin/bash /nix/store/xvfv7xvbdl9njz8q3ay579k323pw9ixs-holochain-wrapper
             └─316 /nix/store/223i4mrvfjjqp7h280fqmq7fwyf2mzzi-holochain-0.4.1/bin/holochain --piped --config-path /nix/store/zqdnp074hkkqvmx105hmr2fjmvzwnra…

Feb 18 20:35:22 holochain holochain-start[316]: ###HOLOCHAIN_SETUP###
Feb 18 20:35:22 holochain holochain-start[316]: ###ADMIN_PORT:1234###
Feb 18 20:35:22 holochain holochain-start[316]: ###HOLOCHAIN_SETUP_END###
Feb 18 20:35:22 holochain holochain-start[316]: 2025-02-18T20:35:22.619323Z  INFO holochain: crates/holochain/src/bin/holochain/main.rs:105: Condu…nitialized.
Feb 18 20:35:22 holochain holochain-start[316]: Conductor ready.
Feb 18 20:35:22 holochain systemd[1]: Started holochain.service.
Feb 18 20:35:34 holochain holochain-start[316]: 2025-02-18T20:35:34.054502Z  INFO kitsune-metric-task: kitsune_p2p_types::metrics: crates/kitsune_p2p/types/s…
Feb 18 20:35:49 holochain holochain-start[316]: 2025-02-18T20:35:49.096513Z  INFO kitsune-metric-task: kitsune_p2p_types::metrics: crates/kitsune_p2p/types/s…
Feb 18 20:36:04 holochain holochain-start[316]: 2025-02-18T20:36:04.141015Z  INFO kitsune-metric-task: kitsune_p2p_types::metrics: crates/kitsune_p2p/types/s…
Feb 18 20:36:19 holochain holochain-start[316]: 2025-02-18T20:36:19.185992Z  INFO kitsune-metric-task: kitsune_p2p_types::metrics: crates/kitsune_p2p/types/s…
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Connection to machine holochain terminated.