Prevent shared accounts from be added as a collaborator on a published form

## Context

As per our terms of use, we do not allow accounts to be created using shared email addresses / shared mailboxes, which is why the following account has been deactivated.

This for 2 main reasons:

1. To limit sharing passwords for the account to protect against breaches.
2. To have a clear record of which public servants had access to the public’s personal information.

## Description

We have alarms in place when an account is created to flag common shared account patterns in #forms-production-events.

We also have a second check in place when someone requests to publish a form / unlocks publishing ability for their account, confirmed not to be a shared account by support.

However there is another way that a shared email address can obtain access to a published form and its responses, by adding a collaborator but not having them be the "publisher" or adding them once the form is published.

Ideally we would close this loophole or have checks in place to prevent this situation