Implementation Plan: Filtering and designating sensitive results in t…

…he API (#996)

* Implementation Plan: Filtering and designating results with sensitive textual content

This IP is still pending an initial experiment to see whether the reindex to create the filtered index can be done in a timely manner. I suspect it will and I was eager to get this idea written out to confirm that, provided reindexing is viable, the rest of the solution is coherent.

* Update filtered index creation description with new information

* Add feasibility section with staging test results

* Update rfcs/detecting_sensitive_textual_content/20230308-implementation_plan_filtering_and_designating_results_with_sensitive_textual_content.md

Co-authored-by: Zack Krida <[email protected]>

* Add changes from review

Co-authored-by: @AetherUnbound, @stacimc, @dhruvkb

* Make clarifications requested by @AetherUnbound

* Add approved reviews

* Update format

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Co-authored-by: Zack Krida <[email protected]>