Retrieve preserve expiry capability via GoCB

Preserve expiry support for GoCB v2 was added in ticket GOCBC-1037 which is going to be used on Sync Gateway for importing documents and keeping the expiry the time. Since preserve expiry is only support on CBS 7.0.0 and above, some way too check if this option is supported, or if to use the old way of manually preserving the expiry would be great.

Is it practical to add this to the SDK as a Capability or expose the server version so we can do this on our side?