[Flow Control] Intra-flow sorting based on user defined stored metadata

[lioraron]

What would you like to be added:
Enable to store and retrieve user defined keys and values per inference request - that can be used by a user implemented intra-flow comparator.
When an inference request is received - enable a user pluggable logic to calculate such user defined keys and values, and store these so that any subsequent invocation of the user's comparator will have access to these keys and values for each inference request in the queue.

Why is this needed:
To enable sorting each flow control queue based on user defined metadata and logic.