Adapting to changes to the publishing platform Maven Central

We publish our libraries on Maven Central where other Android projects can use them. There are some changes:

OSSRH users need to migrate their namespaces to the Central Portal as soon as possible.

https://central.sonatype.org/faq/what-is-different-between-central-portal-and-legacy-ossrh/#self-service-migration

We need to adapt to this and maybe also use the opportunity to upgrade the publishing plugin we use. It may already do the heavy lifting for us.