RFE : Improve secret management doc in OpenShift Pipeline and support Azure KeyVault

Writing your first OpenShift Pipeline/Tekton, you discover that secrets are declared as string in Tasks params and are displayed in clear text in the ARO console.

Request For Enhancement :

1. Improve ARO & OpenShift documentation to describe how to limit secret exposure in the Pipeline
2. Add in the roadmap the integration with Azure KeyVault + the [Azure Key Vault Provider for Secrets Store CSI Driver](https://github.com/Azure/secrets-store-csi-driver-provider-azure)

Note: There is no GitHub Issue page at - [https://github.com/openshift/tektoncd-pipeline](https://github.com/openshift/tektoncd-pipeline)

See also:

- [https://github.com/tektoncd/pipeline/blob/master/docs/tasks.md#using-a-secret-as-an-environment-source](https://github.com/tektoncd/pipeline/blob/master/docs/tasks.md#using-a-secret-as-an-environment-source)
- [https://github.com/tektoncd/pipeline/issues/2343](https://github.com/tektoncd/pipeline/issues/2343)
- [https://github.com/tektoncd/pipeline/issues/3443](https://github.com/tektoncd/pipeline/issues/3443)
- [https://access.redhat.com/documentation/en-us/openshift_container_platform/4.6/html/pipelines/index](https://access.redhat.com/documentation/en-us/openshift_container_platform/4.6/html/pipelines/index)
- [https://docs.openshift.com/container-platform/4.6/pipelines/understanding-openshift-pipelines.html#about-tasks_understanding-openshift-pipelines](https://docs.openshift.com/container-platform/4.6/pipelines/understanding-openshift-pipelines.html#about-tasks_understanding-openshift-pipelines)