Add state stores through StreamBuilder

[ppilev]

Changes:

• [X] state stores can be added to topology though StreamBuilder.AddStateStore

NOTE: It's required to connect state stores to IProcessor<K, V> or ITransformer<K, V, K1, V1> before use it.

Example:

1. Add a state store

       var builder = new StreamBuilder();
       var storeBuilder = Stores.KeyValueStoreBuilder<K, V>(
           Stores.InMemoryKeyValueStore("output-store"),
           new JsonSerDes<K>(),
           new JsonSerDes<V>());
   
       builder.AddStateStore(storeBuilder);

2. Connect the state store with the transformer or processor by passing the store name to storeNames parameter of Process, Transform or TransformValues method:

    builder.Stream<K, V>("topic-name")
           .Transform(
               TransformerBuilder.New<K, V, K1, V1>().Transformer<TTransformer>().Build(), 
               storeNames: "output-store")

3. The state store now can be retrieved in TTransformer.Init and can be used later when TTransformer.Process is called

       public void Init(ProcessorContext<K, V> context)
       { 
           stateStore = (IKeyValueStore<K, V>)context.GetStateStore("output-store");
       }

[LGouellec]

Hi @ppilev ,

Thanks for your contribution. Can you create multiple unit tests to cover your feature please ?

Best regards,