keep track of all persistenceIds that have data in the journal

[rkuhn]

No description provided.

[coreyoconnor]

One option for an implementation of this is a global secondary index with a hash key on persistence ID projecting only the key.

Customers can pursue the GSI implementation with the current schema. Including this in the plugin is, effectively, the same request as #50. The persistenceIds and currentPersistenceIds of a query provider would satisfy this.