Duplicate index issue when importing content

(See CMS-12771 for the discussion, this is the exact same issue)

$CLIENT hits this issue when they create documents via custom JAX-RS endpoints which use WorkflowPersistenceManager.

I created the following codebase which replicates this issue %100 of the time: https://code.onehippo.org/sandbox/index-corruption-issue . I created documentation to reproduce the issue there. TL;DR the /repair-duplicates endpoints work(as a result of CMS-12771), but the creation of duplicates can be avoided to begin with and invoking these on each cluster node is challenging in practice.

See the codebase for details on how to reproduce.