Update renovate config (#36)

Author: trask

.github/renovate.json5

@@ -0,0 +1,16 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "extends": [
+    "config:recommended",
+    "docker:pinDigests",
+    "helpers:pinGitHubActionDigests"
+  ],
+  "packageRules": [
+    {
+      // this is to reduce the number of renovate PRs by consolidating them into a weekly batch
+      "matchManagers": ["github-actions"],
+      "extends": ["schedule:weekly"],
+      "groupName": "github actions"
+    }
+  ]
+}