add unique token filter docs #8451

[AntonEliatra]

Description

add unique token filter docs

Issues Resolved

Closes #8451

Version

all

Checklist

• By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and subject to the Developers Certificate of Origin.
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[github-actions]

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[vagimeli]

@udabhas @varun-lodaya Please provide tech review approval to move this PR forward in the documentation process. Please review this week or provide a peer who can review it. Thank you.