Update get data stream api to indicate that a data stream is in logsdb mode

[martijnvg]

Today the get data stream api does indicate whether a data stream is a tsdb data stream. It returns a top level time_series json object (for data stream element) which includes the time boundary of the tsdb data stream.

When a data stream is in logsdb mode, then the get data stream api doesn't indicate this. I think we should at least add a field that indicates that a data stream is in logsdb mode.

[elasticsearchmachine]

Pinging @elastic/es-storage-engine (Team:StorageEngine)

[elasticsearchmachine]

Pinging @elastic/es-data-management (Team:Data Management)

[parkertimmins]

This appears to be a duplicate of #122486 which has been completed. The GET _data_stream api now includes a field index_mode which can be set to logsdb.