Create Dependabot config file

Created by: dependabot-preview[bot]

👋 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.

Your account was configured to allow an unlimited number of open pull requests. This option is no longer supported in the new config file so it has been changed to 99.

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.

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