feat: make build-docker aware of dockerhub build timestamps

[kelly-sovacool]

Changes

Check whether the built image exists on dockerhub and when the last push occurred.
Only re-build it if the Dockerfile has been updated more recently than the image on dockerhub.

Issues

related to #151

PR Checklist

(Strikethrough any points that are not applicable.)

• This comment contains a description of changes with justifications, with any relevant issues linked.
• Write unit tests for any new features, bug fixes, or other code changes.
• Update docs if there are any API changes.
• Update CHANGELOG.md with a short description of any user-facing changes and reference the PR number. Guidelines: https://keepachangelog.com/en/1.1.0/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.13%. Comparing base (5ed647b) to head (11c2bfd).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #166      +/-   ##
==========================================
+ Coverage   87.53%   89.13%   +1.60%     
==========================================
  Files          11       11              
  Lines         393      451      +58     
==========================================
+ Hits          344      402      +58     
  Misses         49       49              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.