Update cookies.md for clearer regex explanation

[conorbauer23]

Closes #

Summary

Doc Page Title - <Enter a one sentence summation of the pertinent changes (including not-yet-completed work) provided by this PR.>

Effect

The following changes are already committed:

Remaining Work and Prerequisites

The following changes still need to be completed:

• List any outstanding work here

Dependencies and Timing

• Other prerequisites that must be completed before merging this PR

Release:

• When ready
• After date: $DATE

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Post Launch

Do not remove - To be completed by the docs team upon merge:

• Redirect /docs/old-path/ => /docs/new-path/ (if applicable)
• Include/exclude pages ^ respectively within docs search service provider (if applicable)
• For Heroes - add a props post to the discussion board.
• Remove from the project board