Backport of Remove readOnly attrs from Clients Count Config Serializer into release/1.12.x

[hc-github-team-secure-vault-core]

Backport

This PR is auto-generated from #21391 to be assessed for backporting due to the inclusion of the label backport/1.12.x.

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The person who merged in the original PR is:
@Monkeychip
This person should manually cherry-pick the original PR into a new backport PR,
and close this one when the manual backport PR is merged in.

merge conflict error: POST https://api.github.com/repos/hashicorp/vault/merges: 409 Merge conflict []

The below text is copied from the body of the original PR.

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I noticed in the flashMessage displayed after saving the config that the three attrs were mentioned. These are readOnly and thus do not need to be serialized. This is related to the census config work.

While I was in there, I "octane'ified" the serializer.

Backporting to last three supported versions, which misses the 1.11 which had this change. But this was not a functional bug, just cosmetic, so I think that is okay.

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Overview of commits

• 4fd4a06

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