Update build workflow to push to artifact registry

[sjonpaulbrown]

Description

GCR is being deprecated by GCP, and we are migrating our images to Artifact Registry. The following PR updates the builds to be pushed to artifact registry. As part of the migration, the registry endpoint will remain the same as it will continue to be the gcr.io/flow-container-registry endpoint.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 40.95%. Comparing base (0310dfd) to head (75e4bba).
Report is 27 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6810      +/-   ##
==========================================
- Coverage   40.98%   40.95%   -0.03%     
==========================================
  Files        2079     2093      +14     
  Lines      183922   184432     +510     
==========================================
+ Hits        75382    75539     +157     
- Misses     102240   102577     +337     
- Partials     6300     6316      +16     

Flag	Coverage Δ
unittests	40.95% <ø> (-0.03%)	⬇️

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