[WIP] Add Dependabot configuration for Bundler

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

Original prompt

Create a pull request in HealthDataInsight/ndr_avro-lambda that adds Dependabot configuration for Bundler without mentioning the user timgentry.

Requirements:

• Add .github/dependabot.yml if it does not exist.
• Configure Dependabot to check the bundler ecosystem in the repository root (directory: "/").
• Use a weekly schedule (Monday 06:00 UTC) and keep a reasonable open PR limit.
• Add labels dependencies and security.
• Add a commit-message prefix deps and include scope.
• Allow updates for all dependency types.
• Group minor and patch updates into a single group (e.g., ruby-dependencies with patterns "*" and update-types minor and patch).
• Do NOT include reviewers or assignees fields that mention timgentry.

Implementation notes:

• Ensure YAML is valid.
• If .github/ directory does not exist, create it.

Open a PR with an appropriate title (e.g., "Add Dependabot for Bundler") and a short description of what it does and how to adjust cadence/grouping.

This pull request was created from Copilot chat.

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