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
import org.elasticsearch.xpack.core.ml.job.config.Job;
import org.elasticsearch.xpack.core.ml.job.config.JobState;
import org.elasticsearch.xpack.core.ml.job.process.autodetect.state.DataCounts;
import org.elasticsearch.xpack.core.ml.job.results.Bucket;
import org.elasticsearch.xpack.core.ml.utils.Intervals;
import org.hamcrest.Matcher;
import org.junit.After;
import java.time.Duration;
import java.time.Instant;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;
import static org.elasticsearch.xpack.ml.support.BaseMlIntegTestCase.createDatafeed;
import static org.elasticsearch.xpack.ml.support.BaseMlIntegTestCase.createDatafeedBuilder;
import static org.elasticsearch.xpack.ml.support.BaseMlIntegTestCase.createScheduledJob;
import static org.elasticsearch.xpack.ml.support.BaseMlIntegTestCase.getDataCounts;
import static org.elasticsearch.xpack.ml.support.BaseMlIntegTestCase.indexDocs;
import static org.hamcrest.Matchers.equalTo;
import static org.hamcrest.Matchers.greaterThan;
import static org.hamcrest.Matchers.hasSize;
import static org.hamcrest.Matchers.is;
import static org.hamcrest.Matchers.oneOf;
public class DatafeedJobsIT extends MlNativeAutodetectIntegTestCase {
    @After
    public void cleanup() {
        client().admin()