Add dependabot yaml file, enable grouped updates in settings

[jaydonkrooss]

Thank you for contributing to this project!

Describe your problem or feature you'd like added

Enable dependabot updating multiple dependencies, using the grouped updates feature. This card was created to help control dependabot problems we're occasionally seeing (eg. https://github.com/tl-its-umich-edu/my-learning-analytics/security/dependabot/77)

Describe the solution you'd like

This requires a dependabot.yml file in the github folder, THEN enable the grouped updates in the settings (order matters)