Additional / Flexible options for State Store and/or provide API for custom extensions similar to source/sink #1014
Description
Is your feature request related to a problem? Please describe.
It can be desirable to define alternative state stores for persistence in various environments that utilize other data stores outside of RocksDB or a Memory store, both for performance considerations and resiliency. For instance, I would like to use DynamoDB for a state store in our current infrastructure setup.
Describe the solution you'd like
I would like the State Manager to be extended with an API for creating custom state managers, at a minimum - ideally, other default bundled state managers could be included.
Describe alternatives you've considered
Manually writing copies of the state store to other databases as part of the stream processing by copying the state data using the API allowing state access. This would be cumbersome and duplicative.
Additional context
Memory Store and RocksDB aren't for everyone and don't fit every need. Providing an API for extensibility allows for solutions, and doesn't require each potential solution be built and included in the package.