### 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
jobParams.getJobId(),
                    memoryRequirementRefreshListener
                ),
                listener::onFailure
            );
            
            ActionListener<Boolean> getJobHandler = ActionListener.wrap(response -> {
                if (jobParams.getJob().getModelSnapshotId() == null) {
                    modelSnapshotValidationListener.onResponse(true);
                    return;
                }
                client.execute(
                    GetModelSnapshotsAction.INSTANCE,
                    new GetModelSnapshotsAction.Request(jobParams.getJobId(), jobParams.getJob().getModelSnapshotId()),
                    ActionListener.wrap(modelSnapshot -> {
                        if (modelSnapshot.getPage().results().isEmpty()) {
                            modelSnapshotValidationListener.onResponse(true);
                            return;
                        }
                        assert modelSnapshot.getPage().results().size() == 1;
                        if (modelSnapshot.getPage().results().get(0).getMinVersion().onOrAfter(MIN_CHECKED_SUPPORTED_SNAPSHOT_VERSION)) {
                            modelSnapshotValidationListener.onResponse(true);
                            return;
                        }
                        listener.onFailure(
                            ExceptionsHelper.badRequestException(
                                "[{}] job model snapshot [{}] has min version before [{}], "
                                    + "please revert to a newer model snapshot or reset the job",
                                jobParams.getJobId(),
                                jobParams.getJob().getModelSnapshotId(),