### 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/TransportOpenJobAction.java
this.memoryTracker = memoryTracker;
        this.client = new OriginSettingClient(client, ML_ORIGIN);
    }
    @Override
    protected ClusterBlockException checkBlock(OpenJobAction.Request request, ClusterState state) {
        
        
        
        return state.blocks().globalBlockedException(ClusterBlockLevel.METADATA_WRITE);
    }
    @Override
    protected void masterOperation(
        Task task,
        OpenJobAction.Request request,
        ClusterState state,
        ActionListener<NodeAcknowledgedResponse> listener
    ) {
        OpenJobAction.JobParams jobParams = request.getJobParams();
        if (MachineLearningField.ML_API_FEATURE.check(licenseState)) {
            
            ActionListener<NodeAcknowledgedResponse> clearJobFinishTime = ActionListener.wrap(response -> {
                if (response.isAcknowledged()) {
                    clearJobFinishedTime(response, state, jobParams.getJobId(), request.masterNodeTimeout(), listener);
                } else {
                    listener.onResponse(response);
                }
            }, listener::onFailure);
            
            ActionListener<PersistentTasksCustomMetadata.PersistentTask<OpenJobAction.JobParams>> waitForJobToStart =
                new ActionListener<>() {