Configure dependabot bundler updates

Tracks [AINFRA-2437](https://linear.app/a8c/issue/AINFRA-2437).

Adds a Dependabot config that opens a daily bundler PR for the gem's Ruby
dependencies, with minor and patch bumps grouped under
`ruby-minor-and-patch` and the PR limit capped at 5.

The repo is the release-toolkit gem itself, so this configures updates for
its own development and runtime dependencies — it does not consume RT.

---

Generated with the help of Claude Code, https://code.claude.com

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: mokagio

.github/dependabot.yml

@@ -0,0 +1,10 @@
+version: 2
+updates:
+  - package-ecosystem: bundler
+    directory: "/"
+    schedule:
+      interval: daily
+    groups:
+      ruby-minor-and-patch:
+        update-types: [minor, patch]
+    open-pull-requests-limit: 5

CHANGELOG.md

@@ -19,6 +19,7 @@ _None_
 ### Internal Changes
 
 - `openai_ask`: validate named function tools, default to `gpt-4.1`, use `max_completion_tokens`, and opt out of OpenAI request storage. [#719]
+- Configure Dependabot to update Ruby dependencies daily, grouping minor/patch bumps under `ruby-minor-and-patch`.
 
 ## 14.6.0