Allow deletion of identifiers via API

Deletion of identifiers from the customer should be possible via API. I have the following use cases in mind.

1. Anonymize old customer who have requested their account to be deleted. We cannot make the customer anonymous if we cannot clean up their email, phone, cookie ID, ...

2. Delete identifiers that have been added by mistake. Customer could have provided wrong details or there could have been technical issue that has caused an issue with the identifiers.

GDPR delete is not an option to anonymize old customers, because if they want to register again at a later time, their information is kept hidden as long as they use the same identifier.

The events could stay under the customer as they have been linked before the removal of the identifier. If required would be good to have the option to e.g. delete and load them again if required to modify also events in this case.