Enable major upgrades using renovate

Currently renovatebot would only update minor or patch versions of the
container images. This patch adds a preset to let renovatebot propose
major version updates.

renovate.json

@@ -1,7 +1,8 @@
 {
   "$schema": "https://docs.renovatebot.com/renovate-schema.json",
   "extends": [
-    "config:base"
+    "config:base",
+    "docker:enableMajor"
   ],
   "prConcurrentLimit": 5
 }