Add per-binding message type-conversion support

- For the message channels being created, set the corresponding `dataType` and `message-converters` based on the `contentType` value set per-binding
   - This is applicable for both direct-binding and the channels that connect to the binder

spring-cloud-stream-samples/source/src/main/resources/application.yml

@@ -5,7 +5,9 @@ spring:
   cloud:
     stream:
       bindings:
-        output: testtock
+        output:
+          destination: testtock
+          contentType: text/plain
         # uncomment below to use the last digit of the seconds as a partition key
         # hashcode(key) % N is then applied with N being the partitionCount value
         # thus, even seconds should go to the 0 queue, odd seconds to the 1 queue