I also think this informaiton should be part of the wiki of phpbb.com. In light of the new GDPR-law many people/companies publish which cookies they use on their websites in the "cookie policy": As an example: https://mailchimp.com/legal/cookies/
I dont think there is a consensus regarding the GDPR-law actually requires each cookie used to be documented, but before we have seen the first rulings in court, people are cautious and do walk the extra mile. Also it can be seen as a fair and transparent policy.
So - if this is simple, why not just add it to the wiki?!