Backport of updated usage example into release/1.11.x

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

Backport

This PR is auto-generated from #9081 to be assessed for backporting due to the inclusion of the label backport/1.11.x.

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

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I changed the code in the docs for the transit secrets engine example because it assumes that the user is using a bash shell where the <<< redirect will work. I went through the example using the docker image that we publish and that doesn't use a bash shell so it didn't work.

I think using echo and piping into base64 command is much more universal and will work across all of the shells

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Overview of commits

• e9b3351

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