[ML] Missing data frame notifications for create, stop and delete

[sophiec20]

Current notifications for a single data frame batch run as follows, according to 7.2.0-BC2:

Data frame notifications are missing for

• created
• stopped
• deleted

In addition, it might be useful to know it was a pivot transform.

The first message also sounds like an error, when it is going to be happy path. Change from Could not find destination index [df-barcelona-district]. Creating index with deduced mappings.

to

Creating destination index [df-barcelona-district] with deduced mappings.

Once we run continuously, then we should revisit if each checkpoint should have a message, and if we want any stats in there (e.g. checkpoint 123, 15000000 docs indexed)

[elasticmachine]

Pinging @elastic/ml-core