[FEATURE_REQUEST]: KV store to share data between frames

[miguelaeh]

The stage context is read-only by design, mainly because it depends on the language and can contain non-serializable values. This means it cannot be modified from hooks to share data with other frames. Plus, in a distributed setup, the stage context on each node will be independent of the stage context in other nodes.
We could have a global KV instance in the Pipeless node when running on device and use Redis when using distributed mode.

Sharing data between the processing of frames is sometimes useful, thus providing a KV store, that can also be distributed since will contain serializable data only, makes sense.
Also, it should be namespaced by stream id in order to differentiate data from different streams.

Finally, since frames are processed in parallel, it could be a good idea to provide some util functions with this KV store. For example, it could happen that the hook code tries to access data for the previous frame and it is not yet available. The library could provide wait functionality (which would add delay) or error bypass.