[OCPNODE-1671] ImagePolicy uses byte format for base64 fields

[QiWang19]

suggested from openshift/machine-config-operator#4160 (comment).
In the code, we need to use []byte format of base64 data, but []byte will be encoded/decoded when JSON marshal/unmarshal, so set the original field to byte so we do not need to process the data type in the code.

[openshift-ci]

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[openshift-ci]

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API design plays an important part in the user experience of OpenShift and as such API PRs are subject to a high level of scrutiny to ensure they follow our best practices. If you haven't already done so, please review the OpenShift API Conventions and ensure that your proposed changes are compliant. Following these conventions will help expedite the api review process for your PR.

[JoelSpeed]

@QiWang19 Can you please provide a PR description to explain why we are making this change, and link to the initial PR that introduced these fields? Do we have a bug report?

[JoelSpeed]

GoPlayground shows this is a compatible type change from a json serialisation perspective

[QiWang19]

@JoelSpeed update the description #1765 (comment)

[JoelSpeed]

/lgtm

[deads2k]

joel intended for this merge

/approve

[openshift-ci]

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[ART PR BUILD NOTIFIER]

This PR has been included in build ose-cluster-config-api-container-v4.16.0-202402150209.p0.ge741d64.assembly.stream.el9 for distgit ose-cluster-config-api.
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