feat(ci/cd): Set up Hydra

.hydra/jobsets.nix

@@ -0,0 +1,13 @@
+#
+# jobset example file. This file can be referenced as Nix expression
+# in a jobset configuration along with inputs for nixpkgs and the
+# repository containing this file.
+#
+{ ... }:
+let
+  # <nixpkgs> is set to the value designated by the nixpkgs input of the
+  # jobset configuration.
+  pkgs = (import <nixpkgs> {});
+in {
+  hello = pkgs.hello;
+}

.hydra/spec.json

@@ -0,0 +1,22 @@
+{
+  "nixpkgs": {
+    "enabled": 1,
+    "hidden": false,
+    "description": "Nixpkgs",
+    "nixexprinput": "nixpkgs",
+    "nixexprpath": "pkgs/top-level/release.nix",
+    "checkinterval": 300,
+    "schedulingshares": 100,
+    "enableemail": false,
+    "enable_dynamic_run_command": false,
+    "emailoverride": "",
+    "keepnr": 3,
+    "inputs": {
+      "nixpkgs": {
+          "type": "git",
+          "value": "git://github.com/NixOS/nixpkgs.git master",
+          "emailresponsible": false
+      }
+    }
+  }
+}