This PR adds new IProducer as new base interface for IProducer<TKey, TValue>. New interface has single ProduceAsync method that takes all message properties as primitive types include the key and value as pre-serialized bytes.

Compared to existing produce flows this changes:

1. Lets caller serialize key and value up front allowing caller to reuse buffers etc.
2. Avoids the wrapping of all message properties in a temporary Message instance.
3. Avoids the wrapping of produce result properties in an allocated class.