A preview call can be quite expensive and cause timeout in a cluster. As a short term fix we identified 2 (hopefully) small fixes:

- make the call cancellable, the main issue here seems to be that preview calls search without using a parent task id(see this fix for data feeds: https://github.com/elastic/elasticsearch/pull/88142/files#diff-aba58244cb8f9dfa3ac3b6efeb02259e3d5956576f56c1ff5e243dd2aac27381)
- pass the timeout parameter of the preview call to the search call, currently a timeout can be specified, but is ignored for the inner search call, which is executed with no timeout (see https://www.elastic.co/guide/en/elasticsearch/reference/master/search-search.html#search-search-api-query-params).

Both changes are bugs and shall be relatively simple to implement and considered for backport to the 7.17 branch.

@przemekwitek can you have a look at this?

related: #88010
x-pack/plugin/transform/src/test/java/org/elasticsearch/xpack/transform/transforms/pivot/PivotTests.java
"group-B": {
                "terms": {
                  "field": "field-B"
                }
              },
              "group-C": {
                "terms": {
                  "field": "field-C"
                }
              }
            }""";
        GroupConfig groupConfig;
        try (XContentParser parser = createParser(JsonXContent.jsonXContent, groupConfigJson)) {
            groupConfig = GroupConfig.fromXContent(parser, false);
        }
        assertThat(groupConfig.validate(null), is(nullValue()));
        PivotConfig pivotConfig = new PivotConfig(groupConfig, AggregationConfigTests.randomAggregationConfig(), null);
        Function pivot = new Pivot(pivotConfig, new SettingsConfig(), Version.CURRENT, Collections.emptySet());
        assertThat(pivot.getPerformanceCriticalFields(), contains("field-A", "field-B", "field-C"));
    }
    public void testProcessSearchResponse() {
        Function pivot = new Pivot(
            PivotConfigTests.randomPivotConfig(),
            SettingsConfigTests.randomSettingsConfig(),
            Version.CURRENT,
            Collections.emptySet()
        );
        Aggregations aggs = null;
        assertThat(pivot.processSearchResponse(searchResponseFromAggs(aggs), null, null, null, null, null), is(nullValue()));
        aggs = new Aggregations(List.of());