Suggestion responses were previously serialized as streamables which
made writing suggesters in plugins with custom suggestion response types
impossible. This commit makes them serialized as named writeables and
provides a facility for registering a reader for suggestion responses
when registering a suggester.
This also makes Suggestion responses abstract, requiring a suggester
implementation to provide its own types. Suggesters which do not need
anything additional to what is defined in Suggest.Suggestion should
provide a minimal subclass.
The existing plugin suggester integration tests are removed and
replaced with an equivalent implementation as an example
plugin.
The other metric aggregations (min/max/etc) return `null` as their XContent value and string when nothing was computed (due to empty/missing fields). Percentiles and Percentile Ranks, however, return `NaN `which is inconsistent and confusing for the user. This fixes the inconsistency by making the aggs return `null`. This applies to both the numeric value and the "as string" value.
Note: like the metric aggs, this does not change the value if fetched directly from the percentiles object, which will return as `NaN`/`"NaN"`. This only changes the XContent output.
While this is a bugfix, it still breaks bwc in a minor way as the response changes from prior version.
Closes#29066
Clearing the cache indices can be done via GET and POST. As GET should
only support read only operations, this removes the support for using
GET for clearing the indices caches.
* Migrate migration docs from 6.0 to 7.0
Since we only keep one version of migration docs and master is now on 7.0, we
should migrate these so breaking changes can be added in the right place.
* Remove release notes as well
They link to the migration guides, so they have to go.
* Add placeholder notes for 7.0 so doc build is happy
Andy Bristol
Zachary Tong
Nik Everett
Alexander Reelsen
Simon Willnauer
Lee Hinman