👷 Update Renovate bot configuration

Changed the extend configuration from "config:recommended" to
"config:base". Also, enabled auto-merging with a specific prefix for
commit messages, and disabled auto-merging for major versions.

Author: LeoColman

renovate.json

@@ -1,6 +1,11 @@
 {
   "$schema": "https://docs.renovatebot.com/renovate-schema.json",
   "extends": [
-    "config:recommended"
-  ]
+    "config:base"
+  ],
+  "automerge": true,
+  "major": {
+    "automerge": false
+  },
+  "commitMessagePrefix": "⬆"
 }