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
() -> client().execute(GetDatafeedsStatsAction.INSTANCE, statsRequest).actionGet()
                    );
                } else {
                    exception.set(new AssertionError("Job is not deleted"));
                }
            } catch (AssertionError | Exception e) {
                exception.set(e);
            }
        });
        deleteDatafeedThread.start();
        try {
            stopDatafeed(datafeedId);
        } catch (ResourceNotFoundException e) {
            
        } finally {
            deleteDatafeedThread.join();
        }
        if (exception.get() != null) {
            throw exception.get();
        }
    }
    public void testRealtime_GivenProcessIsKilled() throws Exception {
        String jobId = "realtime-job-given-process-is-killed";
        String datafeedId = jobId + "-datafeed";
        startRealtime(jobId);
        KillProcessAction.Request killRequest = new KillProcessAction.Request(jobId);
        client().execute(KillProcessAction.INSTANCE, killRequest).actionGet();
        assertBusy(() -> {
            GetDatafeedsStatsAction.Request request = new GetDatafeedsStatsAction.Request(datafeedId);
            GetDatafeedsStatsAction.Response response = client().execute(GetDatafeedsStatsAction.INSTANCE, request).actionGet();