Added to sprint 15 per discussion at 2022-06-09 sprint planning.

Change 805793 had a related patch set uploaded (by Daimona Eaytoy; author: Daimona Eaytoy):

[mediawiki/extensions/CampaignEvents@master] Add policy acknowledgement to Special:RegisterForEvent

https://gerrit.wikimedia.org/r/805793

Testing notes (for CR and QA): by default there's no policy message. You may want to ensure that this is actually the case, first. Then, if you want to test it with a message, you can create the page MediaWiki:Campaignevents-policy locally with text:

By registering, you agree to the [https://foundation.wikimedia.org/wiki/Terms_of_Use Terms of Use] and [https://foundation.wikimedia.org/wiki/Privacy_policy Privacy Policy].

and then add the following to LocalSettings.php:

$wgHooks['CampaignEventsGetPolicyMessage'][] = static function ( ?string &$msg ) {
	$msg = 'campaignevents-policy';
};

Change 805793 merged by jenkins-bot:

[mediawiki/extensions/CampaignEvents@master] Add policy acknowledgement to Special:RegisterForEvent

https://gerrit.wikimedia.org/r/805793

QA notes above: T309334#8005531

Privacy policy and Terms of use displaying at Special:RegisterForEvent/{id} after following the QA notes at T309334#8005531

T309332#8250907 will cover this ticket @ifried