feat(ci): Add Dependabot configuration for GitHub Actions

[ScottBrenner]

What does this PR do?

Noticed the actions used in the workflows here are outdated, proposing a Dependabot configuration to update - reference https://docs.github.com/en/actions/security-guides/using-githubs-security-features-to-secure-your-use-of-github-actions#keeping-the-actions-in-your-workflows-secure-and-up-to-date

Resolves warnings on workflow runs e.g. https://github.com/roboflow/roboflow-python/actions/runs/33541969237

The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/setup-python@v5

Suggest enabling https://docs.github.com/en/code-security/dependabot/working-with-dependabot/about-dependabot-on-github-actions-runners#enabling-or-disabling-for-your-repository as well

Type of Change

• New feature (non-breaking change that adds functionality)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code where necessary, particularly in hard-to-understand areas
• My changes generate no new warnings or errors
• I have updated the documentation accordingly (if applicable)

Additional Context

Copied from https://github.com/roboflow/supervision/blob/develop/.github/dependabot.yml#L1-L16.