Move rank-eval template compilation down to TransportRankEvalAction
Closes#21777 and #21465
Search templates for rank_eval endpoint so far only worked when sent through
REST end point
However we also allow templates to be set through a Java API call to
"setTemplate" on that same spec. This doesn't go through template execution so
fails further down the line.
To make this work, moved template execution further down, probably to
TransportRankEvalAction.
* Add template IT test for Java API
* Move template compilation to TransportRankEvalAction
This adds support for templating in rank eval requests.
Relates to #20231
Problem: In it's current state the rank-eval request API forces the user to repeat complete queries for each test request. In most use cases the structure of the query to test will be stable with only parameters changing across requests, so this looks like lots of boilerplate json for something that could be expressed in a more concise way.
Uses templating/ ScriptServices to enable users to submit only one test request template and let them only specify template parameters on a per test request basis.
Christoph Büscher
Isabel Drost-Fromm