### Description

This applies to the following APIs:
- [x] open anomaly detection
- [x] start datafeed
- [x] start data frame analytics job
- [x] start trained model deployment

Currently, if the operation takes longer than the configured `timeout`, the response status code is `500`.

With Kibana in mind, a `4xx` response would be more suitable as it will lead to showing more useful information to the user about why the request failed.

Looking at [RFC 9110](https://www.rfc-editor.org/rfc/rfc9110.html#name-408-request-timeout), it seems the most appropriate `4xx` code would be `408 Request Timeout`, even though the RFC describes a different situation. 

The alternative, `504 Gateway Timeout`, would be more appropriate for this situation but it wouldn't improve the user experience in Kibana.
x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportStartDataFrameAnalyticsAction.java
import org.elasticsearch.xpack.core.ml.utils.PhaseProgress;
import org.elasticsearch.xpack.ml.MachineLearning;
import org.elasticsearch.xpack.ml.dataframe.DataFrameAnalyticsManager;
import org.elasticsearch.xpack.ml.dataframe.DataFrameAnalyticsTask;
import org.elasticsearch.xpack.ml.dataframe.MappingsMerger;
import org.elasticsearch.xpack.ml.dataframe.SourceDestValidations;
import org.elasticsearch.xpack.ml.dataframe.extractor.DataFrameDataExtractorFactory;
import org.elasticsearch.xpack.ml.dataframe.extractor.ExtractedFieldsDetectorFactory;
import org.elasticsearch.xpack.ml.dataframe.persistence.DataFrameAnalyticsConfigProvider;
import org.elasticsearch.xpack.ml.dataframe.stats.StatsHolder;
import org.elasticsearch.xpack.ml.extractor.ExtractedFields;
import org.elasticsearch.xpack.ml.job.JobNodeSelector;
import org.elasticsearch.xpack.ml.notifications.DataFrameAnalyticsAuditor;
import org.elasticsearch.xpack.ml.process.MlMemoryTracker;
import org.elasticsearch.xpack.ml.task.AbstractJobPersistentTasksExecutor;
import java.util.Collection;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Optional;
import java.util.Set;
import java.util.function.Predicate;
import java.util.stream.Collectors;
import static org.elasticsearch.core.Strings.format;
import static org.elasticsearch.xpack.core.ClientHelper.ML_ORIGIN;
import static org.elasticsearch.xpack.core.ClientHelper.executeAsyncWithOrigin;
/**
 * Starts the persistent task for running data frame analytics.
 */
public class TransportStartDataFrameAnalyticsAction extends TransportMasterNodeAction<