Some Dependabot Improvements

[desrosj]

This makes several improvements to dependabot.yml.

• Increase the number of concurrent pull requests allowed.
• Add a default cooldown value of 7.
• Configure grouping for GitHub Actions updates.
• Configure npm dependency updates.

[github-actions]

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[Copilot]

Pull request overview

This PR updates the repository’s Dependabot configuration to increase throughput and expand automated update coverage (GitHub Actions + npm), while attempting to add cooldown and grouping behavior.

Changes:

• Raises open-pull-requests-limit from 10 to 20.
• Adds a cooldown default of 7 days.
• Adds grouping configuration and introduces a new npm update configuration.

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