A composable index template with no `template` defined in the body is mistakingly always assumed to not be a time series template. Even if it refers to a component template that has the `index.mode` setting set to `time_series` and the component template defines mappings with dimension fields or routing paths.

Incorrectly this causes to create a data stream with a tsdb index *without* time series start and end time settings set. The fact that this can happen is another bug and is being tracked #98833.

What should happen in this case is that a tsdb data stream is created with a valid tsdb backing index (with correctly generated time series start and end time settings).

This bug was found as part investigating #98792 and is the cause of that bug.
modules/data-streams/src/javaRestTest/java/org/elasticsearch/datastreams/TsdbDataStreamRestIT.java
} catch (Exception | AssertionError e) {
            logger.error("search response body causing assertion error [" + responseBody + "]", e);
            throw e;
        }
    }
    public void testSimulateTsdbDataStreamTemplate() throws Exception {
        var simulateIndexTemplateRequest = new Request("POST", "/_index_template/_simulate_index/k8s");
        var response = client().performRequest(simulateIndexTemplateRequest);
        assertOK(response);
        var responseBody = entityAsMap(response);
        assertThat(ObjectPath.evaluate(responseBody, "template.settings.index"), aMapWithSize(6));
        assertThat(ObjectPath.evaluate(responseBody, "template.settings.index.number_of_shards"), equalTo("2"));
        assertThat(ObjectPath.evaluate(responseBody, "template.settings.index.number_of_replicas"), equalTo("0"));
        assertThat(ObjectPath.evaluate(responseBody, "template.settings.index.mode"), equalTo("time_series"));
        assertThat(ObjectPath.evaluate(responseBody, "template.settings.index.time_series.start_time"), notNullValue());
        assertThat(ObjectPath.evaluate(responseBody, "template.settings.index.time_series.end_time"), notNullValue());
        assertThat(
            ObjectPath.evaluate(responseBody, "template.settings.index.routing_path"),
            containsInAnyOrder("metricset", "k8s.pod.uid", "pod.labels.*")
        );
        assertThat(ObjectPath.evaluate(responseBody, "overlapping"), empty());
    }
    public void testSubsequentRollovers() throws Exception {
        var createDataStreamRequest = new Request("PUT", "/_data_stream/k8s");
        assertOK(client().performRequest(createDataStreamRequest));
        int numRollovers = 16;
        for (int i = 0; i < numRollovers; i++) {
            var rolloverRequest = new Request("POST", "/k8s/_rollover?pretty");
            var rolloverResponse = client().performRequest(rolloverRequest);
            assertOK(rolloverResponse);