Currenlty, we only support default properties for core producer/consumer (spring.cloud.stream.default.producer|consumer...).
These changes add support for configuring default properties for extended producer and consumer properties.
For example, if the binder type is foo, then this allows the applications to configure default properties across
multiple producer or consumer bindings in the form of spring.cloud.stream.foo.default.producer|consumer.property.
The default prefixes for the extended properties are dictated by the respective binder implementations.
Resolves#1360
Manual merging for Map in MergableProperties
Handling values with defaults in extended producer/consumer properties
07b5a691d4