chore: add renovate bot (#46)

Author: SimenB

.github/renovate.json

@@ -0,0 +1,6 @@
+{
+  "extends": ["config:base"],
+  "lockFileMaintenance": { "enabled": true },
+  "rangeStrategy": "replace",
+  "postUpdateOptions": ["yarnDedupeHighest"]
+}