Backport of Typo: Corrected same typo in 2 locations (on-premise to on-premises) into release/1.9.x

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

Backport

This PR is auto-generated from #13402 to be assessed for backporting due to the inclusion of the label backport/website.

WARNING automatic cherry-pick of commits failed. Commits will require human attention.

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

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what it accomplishes: "on-premise" should be "on-premises", since "premise" has a different meaning
how it does so: modified 2 files in the website folder

[hashicorp-cla]

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• yhyakuna
• temp

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[aphorise]

Still pending fix in related 1.9.x section of the docs:

[yhyakuna]

Track this with #16802