Reenable ES support for public/internal project snippets
Background
ES support for public/internal project snippets was added in !18459 (merged), fixing #2358 (closed).
Since this required adding a join field to the ES index this caused #34558 (closed), so we reverted these changes in !19715 (merged).
Proposal
Revert the changes from !19715 (merged), but move them to a new ES mapping version.
This can be done once #10156 (closed) is in place, which will give instance administrators a supported way of upgrading ES index schemas.
Edited by Markus Koller