Attribute `index_type` of `opensearch` in `sink` lacks further explanation

[linghengqian]

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• Attribute index_type of opensearch in sink lacks further explanation. See https://opensearch.org/docs/latest/data-prepper/pipelines/configuration/sinks/opensearch/#configuration-options .

Tells the sink plugin what type of data it is handling. Valid values are custom, trace-analytics-raw, trace-analytics-service-map, or management-disabled. Default is custom.

• This brings up a question: what are the functions of custom, trace-analytics-raw, trace-analytics-service-map and management-disabled? I can't find any documentation explaining them.

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• I hope the documentation can add some explanation.

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