feat: add org-level Renovate preset for Headlamp plugins

All 6 plugin repos use identical Renovate configs. This org-level
preset provides a single source of truth. Plugin repos can extend
it with: "extends": ["local>privilegedescalation/.github:renovate-config"]

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

renovate-config.json

@@ -0,0 +1,19 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "extends": ["config:recommended"],
+  "baseBranches": ["main"],
+  "schedule": ["every weekend"],
+  "prConcurrentLimit": 10,
+  "packageRules": [
+    {
+      "matchManagers": ["npm"],
+      "matchUpdateTypes": ["minor", "patch"],
+      "groupName": "npm minor and patch"
+    },
+    {
+      "matchManagers": ["github-actions"],
+      "matchUpdateTypes": ["minor", "patch"],
+      "groupName": "github-actions minor and patch"
+    }
+  ]
+}