Ensure instructions to build work on arm and amd

[weshayutin]

w/o using dockerx builds the normal docker-build, docker-push failed to work properly as the setup documentation stated on ARM
clusters. This change simply makes the build work more like
oadp-operator.

Why the changes were made

building w/ ARM failed when using
https://github.com/migtools/oadp-non-admin/blob/master/docs/CONTRIBUTING.md

How to test the changes made

Tested w/ both ARM and AMD clusters. :) works

[openshift-ci]

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[kaovilai]

Thoughts on just making multi platform images always? This controller image should be small enough that its going to create productivity not having to ask someone to rebuild for their arch for less than a minute of additional build time.

[weshayutin]

Thoughts on just making multi platform images always? This controller image should be small enough that its going to create productivity not having to ask someone to rebuild for their arch for less than a minute of additional build time.

That is a valid point and one side of the issue. If I recall correctly folks involved in this project perfered to build quickly vs build all arch types ( it was annoying ).

We def do not need to build for ppc or s390.

IIUC, we are building oadp-operator based on the arch of the cluster. Seems like the right pattern to follow here as well.