Use new API from confluentinc/kafka-connect-storage-common#77

[dcsobral]

The API change itself is trivial to adopt. Get the original values, add the defaults, and that's done.

However, many tests either relied on implementation details of the partitioners, or ignored the mechanism used in the very same tests to pass settings in a reliable way and, instead, modified the configuration right before it was passed to the partitioner, which made it unavailable elsewhere as code migrated to relying on HdfsSinkConnectorConfig instead of the no-longer present parsed config map.

[ghost]

@confluentinc It looks like @dcsobral just signed our Contributor License Agreement. :+1:

Always at your service,

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