Max time span allowed in search

[molinaro-m]

Likewise maxSR in the Resource metadata, we'd possibly need a maxTimeSpan for services that want to limit the maximum extent of the searchable time span.

We need to define:

• what unit will it be in: [s]?
• defaults to: no limit?
  (this supposing it will be optional)

Not clear whether this, as well as the full registration prescriptions, should stay in the ConeSearch document or continue to live within SimpleDALRegExt.

[mbtaylor]

Limits get complicated once we have both time and space constraints. In practice a service may be willing to permit searches over all time in a tight cone, but only over a limited time for large area or all-sky queries. Before adding a maxTimeSpan parameter I would suggest to discuss with service providers whether this would in fact be useful. Perhaps something like a service-defined MAXREC limit would be more appropriate.