add dockerhub container registry use

[tarilabs]

... replaces quay.io use in CI/CD/container-registry-use which was available originally through quay.io

Resolves #23

Description

Originally (before Kubeflow code "uplift") quay.io was used for Container Registry; as requested during KF community meeting, this changes to make use of dockerhub as default.

The goal as intended was to keep build infra (makefile, scripts, GHAs) design, but to adapt it to KF community request, while preserving extensibility and customization for any downstream consumer.

How Has This Been Tested?

• dry run (don't have the psw) of make image/build
  results as expected:

docker build . -f Dockerfile -t kubeflow/model-registry:main

• dry run (don't have the psw) of IMG_REGISTRY=quay.io make image/build
  results as expected:

docker build . -f Dockerfile -t quay.io/kubeflow/model-registry:main

• dry run (don't have the pws) of ./scripts/build_deploy.sh
  results as expected:

Building container image..
docker build . -f Dockerfile -t kubeflow/model-registry:cfb4712

• GHAs: this PR will be used.

Merge criteria:

• The commits and have meaningful messages; the author will squash them after approval or will ask to merge with squash.
• Testing instructions have been added in the PR body (for PRs involving changes that are not immediately obvious).
• The developer has manually tested the changes and verified that the changes work

[rareddy]

/approve
/lgtm

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: rareddy, tarilabs

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