Add samples to manage Azure Databricks in Kubeflow Pipelines

[magencio]

This PR adds the following to the samples/contrib folder:

azure-samples/kfp-azure-databricks folder contains a set of Ops which
allow us to manage Azure Databricks resources directly from our Kubeflow
Pipelines.
These Ops leverage Azure Databricks Operator for Kubernetes to manage
those resources. They wrap ResourceOp and abstract pipeline users from
Kubernetes Operator details.
Supported Ops:

• CreateClusterOp, to create a cluster in Databricks.
• DeleteClusterOp, to delete an existing cluster from Databricks.
• CreateJobOp, to create a Spark Job in Databricks.
• DeleteJobOp, to delete an existing Spark Job from Databricks.
• SubmitRunOp, to submit a Job Run in Databricks.
• DeleteRunOp, to delete an existing Run.

azure-samples/databricks-pipelines folder contains several pipeline
samples:

• databricks_operator_*.py samples show how to use ResourceOp to
  manage Databricks resources using Azure Databricks Operator.
• databricks_pkg_*.py samples show how to use Ops in
  kfp-azure-databricks package to do the same.

Additional question to the reviewer:

• Would it be possible to move the code in azure-samples/kfp-azure-databricks to samples/core folder so that the unit tests in that folder are covered by your sample test infra? (https://github.com/kubeflow/pipelines/blob/master/samples/README.md)

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This change is 

[k8s-ci-robot]

Hi @magencio. Thanks for your PR.

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[numerology]

/ok-to-test
Thanks! @magencio

[numerology]

/lgtm
/approve

[k8s-ci-robot]

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