Configure Dependabot for automatic dependency updates

[zhuxiaow0]

Enable Dependabot for Dockerfile and go.mod updates. This will update images in Dockerfile FROM statements, and go modules.

The purpose is to drastically reduce number of vulnerabilities that affect this repo, by keeping dependencies up-to-date.

This PR is created by a script. Please let me know if we should modify any values.

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @zhuxiaow0. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[MrHohn]

/ok-to-test

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: MrHohn, zhuxiaow0

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/kubernetes/dns/blob/master/OWNERS)~~ [MrHohn] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment