Fix the performance of the ps_trace.link view

[jgpruitt]

A user has reported poor performance with the ps_trace.link view.
timescale/promscale#1570

The view provides no way to filter on the link table's start_time. Since the link table is a hypertable based on the start_time, not having a filter on start_time causes a full table scan. I think we need to expose the link's start_time.

[Yamakaky]

Note that it's the same for event. If you don't specify both time and `span_start_time', the respective hypertable get fully scanned. Ideally, adding a filter to one would also add a default filter to the other, but I'm not sure that's possible with views.