[ML] Transform: UI support for writing to a pipeline instead of an index

[hendrikmuhs]

Starting with 7.4 transform allows to write the output into a ingest pipeline instead of a destination index. This is not doable using the UI.

See https://www.elastic.co/guide/en/elasticsearch/reference/7.4/put-transform.html#put-transform-request-body

[elasticmachine]

Pinging @elastic/ml-ui (:ml)

[peteharverson]

The ability to write the output to an ingest pipeline is now possible when editing a transforms, added for 7.10 in #77370.

It is not yet possible to configure this when creating a transform.