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/core/src/test/java/org/elasticsearch/xpack/core/transform/action/PreviewTransformActionRequestTests.java
protected Writeable.Reader<Request> instanceReader() {
        return Request::new;
    }
    @Override
    protected boolean supportsUnknownFields() {
        return false;
    }
    @Override
    protected Request createTestInstance() {
        TransformConfig config = new TransformConfig(
            "transform-preview",
            randomSourceConfig(),
            new DestConfig("unused-transform-preview-index", null),
            null,
            randomBoolean() ? TransformConfigTests.randomSyncConfig() : null,
            null,
            PivotConfigTests.randomPivotConfig(),
            null,
            null,
            null,
            null,
            null,
            null,
            null
        );
        return new Request(config, TimeValue.parseTimeValue(randomTimeValue(), "timeout"));
    }
    public void testParsingOverwritesIdField() throws IOException {
        testParsingOverwrites("", """
            "dest": {"index": "bar","pipeline": "baz"},""", "transform-preview", "bar", "baz");