ci: Add missing CI for feast-operator image builds

[tchughesiv]

What this PR does / why we need it:

Missing CI related to #4145

This change will require that the following image repos are created (if they don't already exist) -

gcr.io/kf-feast/feast-operator
gcr.io/kf-feast/feature-server

Which issue(s) this PR fixes:

#4144

[tchughesiv]

@woop is this something you can help with? the creation of those repos that is.
or, maybe increased perms for @franciscojavierarceo or @jeremyary so they can handle it?

[woop]

Checking this out right now.

[woop]

Just to confirm, is there a reason we'd use kf-feast on GCR instead of dockerhub? Also, @franciscojavierarceo can you confirm what access you have already?

[tchughesiv]

@woop its used in .github/workflows/master_only.yml, which is named "integration-tests-and-build". it appears to run upon PR merge into the master branch and is a way a ensure image builds/pushes are working prior to release.

[franciscojavierarceo]

I have access to Dockerhub but not gcr

[woop]

Hey @franciscojavierarceo you should have GCR access now if you check your GCP console.