add renovate bot

Author: Mic92

renovate.json

@@ -0,0 +1,8 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "extends": ["config:base", ":dependencyDashboard"],
+  "nix": {
+    "enabled": true
+  },
+  "lockFileMaintenance": { "enabled": true }
+}