Add a Dependabot config to auto-update GitHub action versions

[kurtmckee]

Currently, deprecation warnings are being thrown due to actions using out-of-date Node versions (recent example). Rather than submitting a PR to update them manually, this PR configures Dependabot to regularly submit PRs to update GitHub action versions as needed.

If this PR merges, you can expect Dependabot to immediately submit a PR to update actions to newer versions.

PR Checklist

• Tests?
• Docs?
• CHANGELOG updated?
• Issue raised/referenced?

Developers certificate of origin

• I certify that this contribution is covered by the LGPLv2.1+ license as defined in our LICENSE and adheres to the Developer Certificate of Origin.

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📚 Documentation preview 📚: https://mdanalysis--4618.org.readthedocs.build/en/4618/

[github-actions]

Hello there first time contributor! Welcome to the MDAnalysis community! We ask that all contributors abide by our Code of Conduct and that first time contributors introduce themselves on GitHub Discussions so we can get to know you. You can learn more about participating here. Please also add yourself to package/AUTHORS as part of this PR.

[github-actions]

Linter Bot Results:

Hi @kurtmckee! Thanks for making this PR. We linted your code and found the following:

There are currently no issues detected! 🎉

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.44%. Comparing base (347a0c0) to head (816075b).
Report is 25 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #4618      +/-   ##
===========================================
- Coverage    93.59%   93.44%   -0.16%     
===========================================
  Files          168      183      +15     
  Lines        21104    22294    +1190     
  Branches      3919     3930      +11     
===========================================
+ Hits         19752    20832    +1080     
- Misses         894     1002     +108     
- Partials       458      460       +2     

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[RMeli]

Thank you, this looks very useful.

[RMeli]

LGTM. Please add yourself to the authors file if not there already.