[CAL-1725] Activate email verification

[leog]

In order to move forward on letting users create organizations, for which a new email address needs to be provided in order to infer org slug and username slug, we need to verify the ownership of that email address. This will also impact regular users too, as we should verify email addresses in every flow, not just for orgs.

_{From SyncLinear.com | CAL-1725}