Backport of Fix "auto unseal" case inconsistency into release/1.15.x

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

Backport

This PR is auto-generated from #25119 to be assessed for backporting due to the inclusion of the label backport/1.15.x.

:rotating_light:

Warning automatic cherry-pick of commits failed. If the first commit failed, you will see a blank no-op commit below. If at least one commit succeeded, you will see the cherry-picked commits up to, not including, the commit where the merge conflict occurred.

The person who merged in the original PR is: @schavis 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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There was inconsistency in the capitalization of auto unseal in this doc. The initial heading had it right. It shouldn't be capitalized according to the documentation style guidance for feature capitalization. Also, high availability doesn't need to be capitalized.

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Overview of commits

• 07bfa6bd9244a3057a4b9c71377cc23bbb99e3ef

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CI Results: All Go tests succeeded! :white_check_mark:

[schavis]

Applied with manual backport https://github.com/hashicorp/vault/pull/26800