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
}
    }
    private void assertDatafeedStats(String datafeedId, DatafeedState state, String jobId, Matcher<Long> searchCountMatcher) {
        GetDatafeedsStatsAction.Request request = new GetDatafeedsStatsAction.Request(datafeedId);
        GetDatafeedsStatsAction.Response response = client().execute(GetDatafeedsStatsAction.INSTANCE, request).actionGet();
        assertThat(response.getResponse().results(), hasSize(1));
        GetDatafeedsStatsAction.Response.DatafeedStats stats = response.getResponse().results().get(0);
        assertThat(stats.getDatafeedState(), equalTo(state));
        assertThat(stats.getTimingStats().getJobId(), equalTo(jobId));
        assertThat(stats.getTimingStats().getSearchCount(), searchCountMatcher);
    }
    public void testRealtime() throws Exception {
        String jobId = "realtime-job";
        String datafeedId = jobId + "-datafeed";
        startRealtime(jobId);
        try {
            StopDatafeedAction.Response stopJobResponse = stopDatafeed(datafeedId);
            assertTrue(stopJobResponse.isStopped());
        } catch (Exception e) {
            NodesHotThreadsResponse nodesHotThreadsResponse = client().admin().cluster().prepareNodesHotThreads().get();
            int i = 0;
            for (NodeHotThreads nodeHotThreads : nodesHotThreadsResponse.getNodes()) {
                logger.info(i++ + ":\n" + nodeHotThreads.getHotThreads());
            }
            throw e;
        }
        assertBusy(() -> {
            GetDatafeedsStatsAction.Request request = new GetDatafeedsStatsAction.Request(datafeedId);
            GetDatafeedsStatsAction.Response response = client().execute(GetDatafeedsStatsAction.INSTANCE, request).actionGet();
            assertThat(response.getResponse().results().get(0).getDatafeedState(), equalTo(DatafeedState.STOPPED));