ci: group golang deps in renovate

Author: lukasmetzner

renovate.json

@@ -3,5 +3,18 @@
   "extends": [
     "github>hetznercloud/.github//renovate/default",
     "github>hetznercloud/.github//renovate/golang"
+  ],
+  "packageRules": [
+    {
+      "groupName": "golang",
+      "matchDatasources": ["golang-version"]
+    },
+    {
+      "groupName": "golang",
+      "matchPackageNames": [
+        "docker.io/library/golang",
+        "github.com/golang/go"
+      ]
+    }
   ]
 }