Since #87849 and #88534 it is possible that anomaly detection jobs and datafeeds will encounter the `aggregate_metric_double` type.

We need to investigate how this will affect certain aspects of their behaviour:

1. Specifying detector fields when the datafeed is using an aggregation
2. Specifying detector fields when the datafeed is not using an aggregation
3. Ability to switch a datafeed between using an aggregation and not using an aggregation without deleting and recreating the job
4. Correct identification of whether to use `_source` or doc values to get values from `aggregate_metric_double` fields
5. How to appropriately set `summary_count_field` when using `aggregate_metric_double`

Based on this investigation decide what changes we should make to either code or documentation.
x-pack/plugin/ml/qa/native-multi-node-tests/src/javaRestTest/java/org/elasticsearch/xpack/ml/integration/DatafeedJobsIT.java
}
        for (int i = 0; i < numThreads; i++) {
            threads[i].start();
        }
        for (int i = 0; i < numThreads; i++) {
            threads[i].join();
        }
        if (exceptions.isEmpty() == false) {
            throw exceptions.values().iterator().next();
        }
    }
    public void testRealtime_givenSimultaneousStopAndForceDelete() throws Throwable {
        String jobId = "realtime-job-stop-and-force-delete";
        final String datafeedId = jobId + "-datafeed";
        startRealtime(jobId);
        AtomicReference<Throwable> exception = new AtomicReference<>();
        
        
        
        
        
        Thread deleteDatafeedThread = new Thread(() -> {
            try {
                DeleteDatafeedAction.Request request = new DeleteDatafeedAction.Request(datafeedId);
                request.setForce(true);
                AcknowledgedResponse response = client().execute(DeleteDatafeedAction.INSTANCE, request).actionGet();
                if (response.isAcknowledged()) {
                    GetDatafeedsStatsAction.Request statsRequest = new GetDatafeedsStatsAction.Request(datafeedId);
                    expectThrows(
                        ResourceNotFoundException.class,