Add config file for CodeRabbit code review tool

We are testing this as part of an Eficode internal Spike friday event.
https://coderabbit.ai/ is a commercial tool, but has a free plan for open source.
If we like it, we might keep it. If not, this commit can easily be reverted.

.coderabbit.yaml

@@ -0,0 +1,18 @@
+# yaml-language-server: $schema=https://coderabbit.ai/integrations/schema.v2.json
+language: "en-US"
+early_access: false
+reviews:
+  profile: "chill"
+  request_changes_workflow: false
+  high_level_summary: true
+  poem: true
+  review_status: true
+  collapse_walkthrough: false
+  auto_review:
+    enabled: true
+    ignore_title_keywords:
+      - "WIP"
+      - "DO NOT MERGE"
+    drafts: false
+chat:
+  auto_reply: true