=doc #3982 Clarify that EventStream is local only

Devs were confused a few times on the mailing list if the eventstream
publishes to the cluster or not; Suggesting pub-sub if needed in clustered env.
Merge pull request #2125 from ktoso/3982-doc-clarify-eventstream-is-local-ktoso

=doc #3982 Clarify that EventStream is local only