Create Dependabot config file

:wave: Dependabot is moving natively into GitHub! This pull request migrates your configuration from Dependabot.com to a config file, using the new syntax. When you merge this pull request, we'll swap out dependabot-preview (me) for a new dependabot app, and you'll be all set!

With this change, you'll now use the Dependabot page in GitHub, rather than the Dependabot dashboard, to monitor your version updates. Dependabot is now configured exclusively using config files.

If you've got any questions or feedback for us, please let us know by creating an issue in the dependabot/dependabot-core repository.

Learn more about the relaunch of Dependabot

Please note that regular @dependabot commands do not work on this pull request.

:robot::yellow_heart:

As a reminder, Dependabot Preview will be shut down on August 3rd, 2021. You can merge this pull request to migrate to GitHub-native Dependabot. You can read the docs to learn more about what's changing, as well as find out how to get support if you need help migrating.