It seems https://github.com/elastic/elasticsearch/pull/88982 introduced
a dependency on `elasticsearch-grok` to `x-pack-core`. Since the latter
is published to Maven Central, this means consumers will have issues
resolving it's dependencies since `elasticsearch-grok` isn't published.
This pull request resolves this, by adding the publishing plugin to the
`grok` library. We'll then follow up separately to add that to our
release configuration.