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/main/java/org/elasticsearch/xpack/transform/action/TransportPreviewTransformAction.java
boolean requiresRemote = request.getConfig().getSource().requiresRemoteCluster();
        if (TransformNodes.redirectToAnotherNodeIfNeeded(
            clusterState,
            nodeSettings,
            requiresRemote,
            transportService,
            actionName,
            request,
            Response::new,
            listener
        )) {
            return;
        }
        final TransformConfig config = request.getConfig();
        final Function function = FunctionFactory.create(config);
        
        ActionListener<Boolean> validateConfigListener = ActionListener.wrap(
            validateConfigResponse -> useSecondaryAuthIfAvailable(
                securityContext,
                () -> getPreview(
                    config.getId(), 
                    function,
                    config.getSource(),
                    config.getDestination().getPipeline(),
                    config.getDestination().getIndex(),
                    config.getSyncConfig(),
                    listener
                )
            ),
            listener::onFailure