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
{"@timestamp": "$now", "metricset": "pod", "k8s": {"pod": {"name": "hamster", "uid":"947e4ced-1786-4e53-9e0c-5c447e959508", "ip": "10.10.55.1", "network": {"tx": 2005177954, "rx": 801479970}}}}
            {"create": {}}
            {"@timestamp": "$now", "metricset": "pod", "k8s": {"pod": {"name": "cow", "uid":"947e4ced-1786-4e53-9e0c-5c447e959509", "ip": "10.10.55.1", "network": {"tx": 2006223737, "rx": 802337279}}}}
            {"create": {}}
            {"@timestamp": "$now", "metricset": "pod", "k8s": {"pod": {"name": "rat", "uid":"947e4ced-1786-4e53-9e0c-5c447e959510", "ip": "10.10.55.2", "network": {"tx": 2012916202, "rx": 803685721}}}}
            {"create": {}}
            {"@timestamp": "$now", "metricset": "pod", "k8s": {"pod": {"name": "dog", "uid":"df3145b3-0563-4d3b-a0f7-897eb2876ea9", "ip": "10.10.55.3", "network": {"tx": 1434521831, "rx": 530575198}}}}
            {"create": {}}
            {"@timestamp": "$now", "metricset": "pod", "k8s": {"pod": {"name": "tiger", "uid":"df3145b3-0563-4d3b-a0f7-897eb2876ea10", "ip": "10.10.55.3", "network": {"tx": 1434577921, "rx": 530600088}}}}
            {"create": {}}
            {"@timestamp": "$now", "metricset": "pod", "k8s": {"pod": {"name": "lion", "uid":"df3145b3-0563-4d3b-a0f7-897eb2876e11", "ip": "10.10.55.3", "network": {"tx": 1434587694, "rx": 530604797}}}}
            {"create": {}}
            {"@timestamp": "$now", "metricset": "pod", "k8s": {"pod": {"name": "elephant", "uid":"df3145b3-0563-4d3b-a0f7-897eb2876eb4", "ip": "10.10.55.3", "network": {"tx": 1434595272, "rx": 530605511}}}}
            """;
    @Before
    public void setup() throws IOException {
        
        var request = new Request("POST", "/_component_template/custom_template");
        request.setJsonEntity(COMPONENT_TEMPLATE);
        assertOK(client().performRequest(request));
        
        request = new Request("POST", "/_index_template/1");
        request.setJsonEntity(TEMPLATE);
        assertOK(client().performRequest(request));
    }
    public void testTsdbDataStreams() throws Exception {
        assertTsdbDataStream();
    }
    public void testTsdbDataStreamsNanos() throws Exception {