add micro-batching to batch processor

[RafalSkolasinski]

Add micro-batching functionality to batch processor:

• user able to provide new parameter: micro-batch size
• batch processor to combine single prediction instances into batch
• send batch as single request
• split prediction results into single instances to maintain parity with not micro-batching mode

Benefits:

• lower network overhead
• possibility to benefit from vectorized implementations of underlying inference library