Improve our consent form for user research

Originally created by @sajolida on #16534 (Redmine)

Until now we’ve used the Simply Secure Bill of Rights but it’s quite basic. Bernard Tyers shared better forms with me and we should adapt them and put up on our website.

Also: https://www.userfocus.co.uk/articles/anatomy-of-a-consent-form.html

Related issues

Blocks #17580 (closed)

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