ahmed: Factor configuration.nix into smaller submodules

I checked that this didn't result in any (non-trivial) changes like so:

$ vi hosts/ahmed/configuration.nix
$ nixos-rebuild build --flake .#ahmed
$ nix-diff /run/current-system ./result

1 files changed, 27 insertions, 0 deletions

diff --git a/hosts/ahmed/minecraft/default.nix b/hosts/ahmed/minecraft/default.nix
new file mode 100644
index 0000000..112ef8f
--- /dev/null
+++ b/hosts/ahmed/minecraft/default.nix
@@ -0,0 +1,27 @@
+# This module configures a Minecraft server.
+#
+# Most of the heavy lifting is done in the reusable module `modules/nixos/on-demand-minecraft/`.
+{pkgs, ...}: {
+  # Set up Minecraft server.
+  services.on-demand-minecraft = {
+    enable = true;
+    eula = true;
+
+    package = pkgs.unstable.papermc;
+
+    openFirewall = true;
+
+    # Try shutting down every 10 minutes.
+    frequency-check-players = "*-*-* *:00/10:00";
+
+    # Seed requested by Tobias.
+    server-properties."level-seed" = "1727502807";
+
+    # I changed the default location after creating the world.
+    data-dir = "/srv/minecrafter/papermc-1.21.4-15";
+  };
+
+  # Update the DDNS.
+  # This would be the "IP" we give to folks.
+  services.cloudflare-dyndns.domains = ["minecraft.linus.onl"];
+}