feat: add headscale

Headscale is an open source implementation of the tailscale server.
We've written a module that will allow you to easily run it with some
basic but sensible options, and set it up for running on a1d1.

Change-Id: If67dd498cbe0b0c3c81c66a0216845d0eaf1282c
Reviewed-on: https://git.clicks.codes/c/Infra/NixFiles/+/728
Tested-by: Samuel Shuert <coded@clicks.codes>
Reviewed-by: Samuel Shuert <coded@clicks.codes>
diff --git a/systems/x86_64-linux/a1d1/headscale.sops.json.license b/systems/x86_64-linux/a1d1/headscale.sops.json.license
new file mode 100644
index 0000000..bda0f14
--- /dev/null
+++ b/systems/x86_64-linux/a1d1/headscale.sops.json.license
@@ -0,0 +1,3 @@
+SPDX-FileCopyrightText: 2024 Clicks Codes
+
+SPDX-License-Identifier: GPL-3.0-only