Migrate from OSSRH service to Central Publisher Portal

[ppatierno]

The OSSRH service we use for pushing the artifacts withing Nexus repository manager will reach end-of-life on June 30th, 2025. They have the announcement when you log into the legacy service we use right now. We should migrate to the new one which can be done through the Central support. More details here https://central.sonatype.org/news/20250326_ossrh_sunset/

The main changes to make at project level are:

• replacing the nexus-staging-maven-plugin with the central-publishing-maven-plugin (more info about the new plugin here)
• removing the snapshotRepository
• updating the Azure scrips settings.xml and the corresponding job to deploy Strimzi artifacts

An example of migration can be found here

The migration of the io.strimzi namespace together with the generation of the new CENTRAL_USERNAME and CENTRAL_PASSWORD (using token generation feature) are not in the scope of this issue.
We'll do them out of band together with updating the Azure pipelines configuration within the Azure portal.