Add Dependabot auto-merge workflow

[Marenz]

Summary

• Add GitHub workflow to automatically approve and merge Dependabot PRs
• Uses merge method for clean commit history

[Copilot]

Pull Request Overview

This PR introduces an automated workflow to streamline dependency updates by automatically approving and merging Dependabot pull requests using GitHub Actions.

Key Changes:

• New GitHub Actions workflow that triggers on pull requests from Dependabot
• Configured to use merge commits for maintaining a linear commit history

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_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[Copilot]

This workflow auto-merges all Dependabot PRs without any checks. Add a condition to require passing CI checks before merging, such as adding needs: [test] or checking for required status checks to prevent merging broken dependencies.

[Copilot]

The default GITHUB_TOKEN may lack sufficient permissions to approve and merge PRs. Consider using a personal access token (PAT) or GitHub App token with appropriate permissions stored in secrets, such as ${{ secrets.DEPENDABOT_PAT }}.

Suggested change

	github-token: ${{ secrets.GITHUB_TOKEN }}
	github-token: ${{ secrets.DEPENDABOT_PAT }}