feat(renovate.json): add a basic Renovate configuration file

This will help us keep versioned Docker tags up to date without much intervention other than merging PRs and deploying configurations.

renovate.json

@@ -0,0 +1,7 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "assignees": ["dr460nf1r3"],
+  "commitMessageAction": "update",
+  "extends": ["config:base", ":gitSignOff"],
+  "reviewersFromCodeOwners": true
+}