feat: add Renovate dependency update config

Extends the shared CartSnitch Renovate preset from cartsnitch/.github.
Minor/patch automerge, major requires review, dependency PRs labeled and grouped.

Co-authored-by: Deploy Debbie <debbie@cartsnitch.com>
Co-authored-by: Paperclip <noreply@paperclip.ing>

renovate.json

@@ -0,0 +1,4 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "extends": ["local>cartsnitch/.github:renovate-config"]
+}