Add Dependabot Auto Manage workflow

[Marenz]

Summary

• Add GitHub Actions workflow to automatically approve and merge Dependabot PRs
• Uses ad/dependabot-auto-approve action with merge method
• Applies to all dependency types and adds 'auto-merged' label

[Copilot]

Pull Request Overview

Adds a GitHub Actions workflow to automatically approve and merge Dependabot pull requests, streamlining dependency updates with minimal manual intervention.

• Introduces automated approval and merging for all Dependabot PRs
• Configures the workflow to trigger on pull request events with proper permissions
• Sets up labeling for auto-merged PRs to maintain visibility

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[Copilot]

Using 'pull_request' trigger allows external contributors to trigger this workflow. Consider using 'pull_request_target' with additional safety checks, or restrict to specific event types like 'opened' and 'synchronize'.

Suggested change

	on: pull_request
	on:
	pull_request:
	types: [opened, synchronize]

[Marenz]

Seems the settings for allowed actions need to be updated to make this one work:

The action ad/dependabot-auto-approve@v1 is not allowed in frequenz-floss/frequenz-client-reporting-python because all actions must be from a repository owned by frequenz-floss, created by GitHub, verified in the GitHub Marketplace, or match one of the patterns: PyO3/maturin-action@, brettcannon/check-for-changed-files@, yoheimuta/action-protolint@*.