Export Inspector: allow selecting of root directory for pvserver configs

This is extracted from #19073 (closed)

step 1: let's get the "export now" working, however clunky. For remote connections, we accept two separate Root Directories, one for client side and one for server side. Data Extracts will export using the server-side root directory while Image Extracts including cinema/png/etc. will use the client side root directory.