Provide a way to retrieve the external ID for creating archive logs export to s3

[michelmorin]

To create an archive logs to s3, you require a unique external ID for that sub account. Currently, the only way to get this string, is by logging into the logzio UI and copy the external ID string. Ideally, we would like to have this available as an output of the logzio_subaccount resource, so we can use this in creation of the archive_logs using the logzio_archive_logs resource.

I also, couldn't find a way to retrieve this string from calling the Logzio API at https://docs.logz.io/api/

It seems the AWS Account ID is static and doesn't change, but it probably makes sense to have this retrievable also as output of the logzio_subaccount as well