[records] sort by updated

[pvgenuchten]

Description

When sorting on '-updated' on ogcapi-records, a random order is returned, maybe due to a combination of sorting on modification_date and date_revision or date?

On demo the effect is less obvious because only 2 dates exist, but
https://demo.pycsw.org/gisdata/collections/metadata:main/items?sortby=-updated&offset=100 returns same order as https://demo.pycsw.org/gisdata/collections/metadata:main/items?sortby=updated&offset=100

Steps to Reproduce

load some data with various dates populated, oreder by updated

Additional Information

relevant code seems

pycsw/pycsw/core/repository.py

Line 151 in c532be3

'updated': self.dataset.insert_date,

insert-date is the same for most of my content, because i imported all records at a single moment, expected would be that the modified-date of the metadata record itself was used (or if empty, insert-date), this logic is also applied in

pycsw/pycsw/ogc/api/records.py

Line 1177 in c532be3

record_dict['properties']['updated'] = record.date_modified

, which explains the difference

the problem here is that date-modified is not always populated, can we populate it at insert if nill?

alternative solution display dataset date and order by dataset date (which is usually more relevant, but not always populated)

see #365