Update POM to use Sonatype's Central Portal for Maven Releases

[tdonohue]

References

This PR is a port of DSpace/DSpace#10986 , specific to DSpace/dspace-replicate.

Description

As of June 30, 2025, Sonatype has retired their older OSSRH system used to release Maven modules to Maven Central. The replacement is their new "Central Portal"

https://central.sonatype.org/pages/ossrh-eol/

This PR updates our Parent POM to use the new Central Portal for releases, following their documented guidelines: https://central.sonatype.org/publish/publish-portal-guide/

See DSpace/DSpace#10986 for more details.

WARNING: This is untested, but the only way to fully test it is to "cut" a new release. I have tested this code in several -SNAPSHOT releases of DSpace/DSpace though and it has worked well. Release procedure has also been updated: https://wiki.lyrasis.org/display/DSPACE/Release+Procedure

[tdonohue]

Merging this immediately as it passes automated checks. As noted, the only way to fully test this is to cut a new release. So, there's always a slight chance we'll find issues in our next release(s)...but, if so, I'll send another PR to this project.

In any case, there's no harm in merging this PR. The old release system is gone/disabled now, so we have to move to Sonatype's Central Portal