This addresses an issue reported on the Forum where `API Unexpected Data`
warnings are appearing in the system logs for the `thread_entry_recipients`
and `system_emails` keys for piped emails. This is due to the API request
validator that checks the keys of the API data; if a key's data is an array
itself it loops through the validator again to check the key(s) inside the
data array. This is fine for most keys but for the `thread_entry_recipients`
and `system_emails` keys the request structure does not contain the
necessary sub-keys to validate the data keys. This adds the necessary
sub-keys to the request structure so that `thread_entry_recipients` and
`system_emails` data keys can be validated.