.github: enable renovate

Author: nikstur

.github/renovate.json

@@ -0,0 +1,15 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "extends": [
+    "config:base",
+    "group:all",
+    "schedule:monthly"
+  ],
+  "dependencyDashboard": false,
+  "lockFileMaintenance": {
+    "enabled": true
+  },
+  "nix": {
+    "enabled": true
+  }
+}