use dependabot for dockerfiles

[grokspawn]

Description of the change:

Motivation for the change:

Reviewer Checklist

• Implementation matches the proposed design, or proposal is updated to match implementation
• Sufficient unit test coverage
• Sufficient end-to-end test coverage
• Docs updated or added to /docs
• Commit messages sensible and descriptive

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 48.23%. Comparing base (ced4d17) to head (ba7de0c).
Report is 12 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1434      +/-   ##
==========================================
+ Coverage   48.14%   48.23%   +0.08%     
==========================================
  Files         136      136              
  Lines       12780    12805      +25     
==========================================
+ Hits         6153     6176      +23     
- Misses       5592     5594       +2     
  Partials     1035     1035              

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[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: grokspawn, joelanford

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