Deal with several account cancellation issues
The commits in this MR achieve:
Do not allow to delete an account if there are pending orders.
When deleting a middleware account do not remove the WC account but disable it in practice by resetting password and setting contact email to LDH provided email.
Also remove all PII in WC account, orders and subscriptions.
delete_user CLI command also checks for pending orders before deleting an account.
user.usernamewhen checking if recovery email is already used in WC.