We were seeing more and more common fields between "regular" backing indices and failure store indices (i.e. `indices`, `rolloverOnWrite`, `autoShardingEvent`). To avoid having to duplicate these fields (and possibly any future fields), we extract a class that contains these fields.
Adds the ability to configure a data stream to create a new kind of backing index called a failure store which will eventually be used to store error information when ingest pipelines fail to ingest a document or when a document fails to be parsed correctly by the configured mapping on the data stream.
