Update renovate.json

Reviewed-on: coop-cloud/taiga#2

renovate.json

@@ -0,0 +1,14 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "extends": [
+    "config:recommended"
+  ],
+  "packageRules": [
+    {
+      "matchDatasources": [
+        "docker"
+      ],
+      "pinDigests": true
+    }
+  ]
+}