counter: 1.3.1 - Refined `CounterStreamProcessor` (serde-config)

* Refactored the creation of the ``JsonSerde``s, that are used to consume
  the incomming messages.
* All special ``Serdes``, that are used for incomming and outgoing messages,
  are created in separted methods now.
* Removed unnecessary operatorx in the ``Materialized``-configuration for
  the state store (the operator is not necessary, because no headers are
  present, when deserializing from a store).