Add overlay to support Azure Database for MySQL

[yilun-msft]

Which issue is resolved by this Pull Request:
Resolves #

Description of your changes:
Create an Azure metadata overlay to use Azure MySQL and provide a readme.md as the instruction. Detailed instruction would be seen in the Readme.md. This would enable Azure MySQL user to use Azure MySQL as the metadata db.

Checklist:

• Unit tests have been rebuilt:
  1. cd manifests/tests
  2. make generate-changed-only
  3. make test

[kubeflow-bot]

This change is 

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[yilun-msft]

@googlebot I signed it!

[yilun-msft]

/assign @eedorenko, @sudivate, @shbijlan

[eedorenko]

I think we need:

• Copy content of metadata/overlays/azure to stacks/azure/metadata so we keep everything Azure specific in one folder.
• Reference stacks/azure/metadata from kustomization.yaml. Perhaps optionally (aka uncomment this if you want to use ...)
• Update installation guide on the Kubeflow website with what you have in Readme.md.

[eedorenko]

/assign eedorenko

[yilun-msft]

I think we need:

• Copy content of metadata/overlays/azure to stacks/azure/metadata so we keep everything Azure specific in one folder.
• Reference stacks/azure/metadata from kustomization.yaml. Perhaps optionally (aka uncomment this if you want to use ...)
• Update installation guide on the Kubeflow website with what you have in Readme.md.

Eugene, do you mean move metadata/overlays/azure to stacks/azure/metadata or copy them? I will go ahead and document them in kubeflow/website

[eedorenko]

I mean move.

[yilun-msft]

A meta comment on how the validation is done: I created an Azure Database for MySQL: kf-test.mysql.database.azure.com and edit the kustomization to use ./metadata as instructed in the Readme.md. Execute a pipeline and verify the metadata changes in the selected database named "mlmetadata"

[eedorenko]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: eedorenko, yilun-msft

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