Backport of Docs: GCP SA clarity. Resolved merge conflict. Closes: #12231. into release/1.11.x

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

Backport

This PR is auto-generated from #16787 to be assessed for backporting due to the inclusion of the label backport/1.11.x.

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

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Missed merger (from: #12231) with good clarity notes that still relevant to: vaultproject.io/docs/auth/gcp - please merge.

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Overview of commits

• fb9b01b2a41e9e98f2e1f0a4c03770413065f0fc