Data Transporter - SFTP ssh key should be pem format

[lp-tattwell]

https://knowledge.liveperson.com/data-reporting-analytics-data-transporter-user-guide.html

On that page, it isn't stated that the SFTP SSH key should be in pem format when added to the platform. Configuring SFTP with SSH will fail if the key is not in pem format.

In addition, it is not 100% clear whether we support open OPENSSH. If we don't, then it should be stated here that we don't.