Bulk API ignores ingest pipeline for bulk update items

[martijnvg]

The pipeline defined in the bulk update item here is ignored:

POST /_bulk
{"update":{"_id":"1","_index":"pipeline-test","pipeline":"lowercase-pipeline"}}
{"upsert":{"myField":"UPPER"},"script":{"source":"ctx._source.myField = 'CHANGED'","lang":"painless"}}

Only if the pipeline is defined as query string argument, then the pipeline is picked up and used to process the upset:

POST /_bulk?pipeline=lowercase-pipeline
{"update":{"_id":"1","_index":"pipeline-test"}}
{"upsert":{"myField":"UPPER"},"script":{"source":"ctx._source.myField = 'CHANGED'","lang":"painless"}}

The Bulk API should also use the pipeline defined in the bulk update item.

[elasticmachine]

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