Verify Phone Numbers on Signup

### Epic

_No response_

### Description

As an admin

I want to require users to verify a phone number when they register

So that I can limit abuse

In a free platform with self registration the potential exists for a user to create multiple accounts, just requiring a unique email is probably not sufficient for to manage this.

Plugging in a service like https://www.vonage.com/communications-apis/verify/ or using a generic SMS provider would allow us to require a phone number and then check for other existing accounts.

This is lower friction that cards/billing but higher than just email

It could also be used for 2FA in future

### Acceptance Criteria

- [ ] criteria 1
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