Datahub plugin / configuration is invalid if GeoNetwork is not deployed on the `/geonetwork/` context

[jahow]

Describe the bug

See #9056 (comment)

The code here assumes that GN is deployed on /context/:

core-geonetwork/plugins/datahub-integration/src/main/java/org/fao/geonet/datahub/DatahubController.java

Line 188 in 812168c

.replace("[global]", "[global]\ngeonetwork4_api_url = \"/geonetwork/" + portalName + "/api\"");

This means that if GeoNetwork is deployed on another context, the Datahub interface will not function properly.