Add "IsEnded" reporting option for sessions to Reports API

From CW-7594073

When using the Reports Manager Extension in 5.5, there is no easy way to identify a session that has been ended using the options available. When creating extensions, sessions have the "IsEnded" property, which would be very helpful for the reports manager to be able to access, to be able to get reports on only those sessions that have not been Ended. This appears to be missing from the API itself, and not just the extension.