clarify GDC metadata archive zipfile composition

[tomkralidis]

Given GDC is required to provide a metadata archive zipfile, provide additional details on the composition of the zipfile. This was raised during WIS2 Global Services testing in September 2024 where Canada and Germany GDC produced a zipfile with all WCMP2 records at the "root" of the zipfile (when unzipped) and CMA GDC enclosed the same in a directory named after the GDC centre id.

There is value in the CMA GDC approach to be able to "self identify" a given archived when unzipped using a directory:

|____cn-cma-global-discovery-catalogue
| |____int-eumetsat-serviri-core.json
| |____ca-eccc-msc-gdc.global-discovery-catalogue.json
| |____cn-cma.nmic.prediction-forecast.json
| |____de-dwd.icon-eps-all.json

Note that we do not/will not provide any provisions on the filename of each WCMP2 document.

[amilan17]

@tomkralidis marked as an revision to the original FT2024-2 amendments based on feedback received during NFP period of review.