Offset metadata should not be lost in case of batch reprocessing

[frosiere]

Issue #2170 introduced a way to control the metadata associated to an offset but in case of exception during the processing of a batch, these metadata are no present anymore when records are reprocessed.

So, in this issue, we will ensure these metadata are not lost in such a case.

Javadoc of OffsetAndMetadataProvider has also been reviewed as this provider is used for both, sync and async commits.