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
.get();
        String indexName = "stop-restart-data";
        client().admin().indices().prepareCreate("stop-restart-data").setMapping("time", "type=date").get();
        long numDocs = randomIntBetween(32, 2048);
        final long intervalMillis = TimeValue.timeValueHours(1).millis();
        long now = System.currentTimeMillis();
        long oneWeekAgo = now - 604800000;
        long twoWeeksAgo = oneWeekAgo - 604800000;
        indexDocs(
            logger,
            indexName,
            1,
            Intervals.alignToCeil(twoWeeksAgo, intervalMillis),
            Intervals.alignToCeil(twoWeeksAgo, intervalMillis) + 1
        );
        indexDocs(
            logger,
            indexName,
            numDocs - 1,
            Intervals.alignToCeil(twoWeeksAgo, intervalMillis) + intervalMillis,
            Intervals.alignToFloor(oneWeekAgo, intervalMillis)
        );
        long numDocs2 = randomIntBetween(32, 2048);
        indexDocs(
            logger,
            indexName,
            numDocs2,
            Intervals.alignToCeil(oneWeekAgo, intervalMillis),
            Intervals.alignToFloor(now, intervalMillis)
        );