rate aggregation should support being a sub-aggregation
of a composite agg.
The catch is that the composite aggregation source
must be a date histogram. Other sources can be present
but their must be exactly one date histogram source
otherwise the rate aggregation does not know which
interval to compare its unit rate to.
closes https://github.com/elastic/elasticsearch/issues/76988
This replaces the `script` docs for bucket aggregations with runtime
fields. We expect runtime fields to be nicer to work with because you
can also fetch them or filter on them. We expect them to be faster
because their don't need this sort of `instanceof` tree:
a92a647b9f/server/src/main/java/org/elasticsearch/search/aggregations/support/values/ScriptDoubleValues.java (L42)
Relates to #69291
Co-authored-by: James Rodewig <40268737+jrodewig@users.noreply.github.com>
Co-authored-by: Adam Locke <adam.locke@elastic.co>
In some cases when the rate aggregation is not a child of a date histogram
aggregation, it is not possible to determine the actual size of the date
histogram bucket. In this case the rate aggregation now throws an exception.
Closes#63703
