Added support of building nfsclient arm64 docker images

[kopwei]

Current RPi OS and Ubuntu Focal for RPi both support ARM64 arch. In order to run the container on RPi with 64bit OS, we need to have ARM64 compatible images.

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[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: To complete the pull request process, please assign jsafrane You can assign the PR to them by writing /assign @jsafrane in a comment when ready.

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[kopwei]

/assign @jackielii

[k8s-ci-robot]

@kopwei: GitHub didn't allow me to assign the following users: jackielii.

Note that only kubernetes-incubator members, repo collaborators and people who have commented on this issue/PR can be assigned. Additionally, issues/PRs can only have 10 assignees at the same time. For more information please see the contributor guide

In response to [this](https://github.com/kubernetes-incubator/external-storage/pull/1331#issuecomment-643794836): >/assign @jackielii Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes/test-infra](https://github.com/kubernetes/test-infra/issues/new?title=Prow%20issue:) repository.

[kopwei]

/assign @jsafrane

[kmova]

@kopwei We are in the middle of migrating the NFS client code into a new home under https://github.com/kubernetes-sigs/nfs-subdir-external-provisioner. The migration PR is up for review at the moment. https://github.com/kubernetes-sigs/nfs-subdir-external-provisioner/pull/2

Can I circle back with you to get to PR raised on the new repo once the above migration PR is merged?

[kopwei]

@kmova , sure, it is not urgent :-)

[nikhita]

As @kmova mentioned, we are in the process of archiving this repo and continuing work in https://github.com/kubernetes-sigs/nfs-subdir-external-provisioner. Please reopen a PR in the new repo once https://github.com/kubernetes-sigs/nfs-subdir-external-provisioner/pull/2 has merged. Thanks for your patience! :)

Going to close this PR in order to be able to archive this repo.