Create a new "cancel signups" permission to split "administer signups"

Canceling signups is a destructive operation. Especially if the signup form has fields, you're losing data entered by the user. Now that #55168: tracking actual attendance is in, I can easily see situations where a site might want to empower a role to be able to record attendance at events, but not necessarily give them power to destroy signup data by canceling signups. So, it seems like splitting the cancel powers off of the usual "adminster signups" permission into a separate "cancel signups" perm.