Support for arm64 in simple-pbt image

[tenzen-y]

Signed-off-by: tenzen-y yuki.iwai.tz@gmail.com

What this PR does / why we need it:
I modified the Dockerfile for simple-pbt to support arm64 and I have tested on my local using the below commands:

• linux/arm64

docker run -it --platform linux/arm64 ytenzen/multiplatform-simple-pbt:latest --epochs=10

• linux/amd64

docker run -it --platform linux/amd64 ytenzen/multiplatform-simple-pbt:latest --epochs=10

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Part-of #1900

Checklist:

• Docs included if any changes are user facing

[coveralls]

Coverage increased (+0.1%) to 73.545% when pulling 405399a on tenzen-y:support-for-arm64-in-simple-pbt-image into 58a3f4b on kubeflow:master.

[johnugeorge]

/lgtm
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: johnugeorge, tenzen-y

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