The SchedulerEngine is used in several places in our code and not all
of these usages properly stopped the SchedulerEngine, which could lead
to test failures due to leaked threads from the SchedulerEngine. This
change adds stopping to these usages in order to avoid the thread leaks
that cause CI failures and noise.
Closes#38875
The data frame plugin allows users to create feature indexes by pivoting a source index. In a
nutshell this can be understood as reindex supporting aggregations or similar to the so called entity
centric indexing.
Full history is provided in: feature/data-frame-transforms
