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
@Before
    public void setupClient() {
        if (client != null) {
            client.close();
        }
        client = new MyMockClient(getTestName());
    }
    @After
    public void tearDownClient() {
        client.close();
    }
    @Override
    protected NamedXContentRegistry xContentRegistry() {
        return namedXContentRegistry;
    }
    public void testValidateExistingIndex() throws Exception {
        SourceConfig source = new SourceConfig("existing_source_index");
        Function pivot = new Pivot(getValidPivotConfig(), new SettingsConfig(), Version.CURRENT, Collections.emptySet());
        assertValidTransform(client, source, pivot);
    }
    public void testValidateNonExistingIndex() throws Exception {
        SourceConfig source = new SourceConfig("non_existing_source_index");
        Function pivot = new Pivot(getValidPivotConfig(), new SettingsConfig(), Version.CURRENT, Collections.emptySet());
        assertInvalidTransform(client, source, pivot);
    }
    public void testInitialPageSize() throws Exception {
        int expectedPageSize = 1000;
        Function pivot = new Pivot(
            new PivotConfig(GroupConfigTests.randomGroupConfig(), getValidAggregationConfig(), expectedPageSize),
            new SettingsConfig(),