Add support for updatedAfter to metadata queries

[sosna]

When querying for data, a client has the possibility to indicate that it wants to retrieve what has changed since a certain point in time.

It would be nice to add a similar feature to metadata queries.

The fact that metadata messages do not have the equivalent of a dataset action might be an issue, though.

[agent96]

One thing to think about, does the updatedAfter propegate to the descendants. For example if I query for a Codelist with updatedAfter=2012&references=descendants, teh DSD was not updated since this time, but a codelist used by the DSD was updated after this period, should it return the Codelist?

[sosna]

Good point indeed! It sounds logical to me that updatedAfter applies to anything matching the query. On the other hand, asking for a datastructure resource and then getting a response without any datastructure in it, but only codelists does not seem ideal...

[stratosn]

Would this issue potentially include adding such information (i.e. lastUpdated) in the Maintainables?

[sosna]

We might want to rethink the use cases again and see whether existing HTTP features (like conditional GET requests) might be sufficient.