Update known issues for DT and Import/Export

What does this MR do and why?

re: #478819 (closed)

Updates the known issues section for Direct Transfer and Import/Export with a note that epic's and work item's authors are not being mapped to the original author but to the importing user in 17.0, 17.1 and 17.2

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

N/A

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Related to #478819 (closed)