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.
qa/rolling-upgrade/src/test/java/org/elasticsearch/upgrades/UpgradeClusterClientYamlTestSuiteIT.java
protected boolean preserveIndicesUponCompletion() {
        return true;
    }
    @Override
    protected boolean preserveReposUponCompletion() {
        return true;
    }
    @Override
    protected boolean preserveTemplatesUponCompletion() {
        return true;
    }
    public UpgradeClusterClientYamlTestSuiteIT(ClientYamlTestCandidate testCandidate) {
        super(testCandidate);
    }
    @ParametersFactory
    public static Iterable<Object[]> parameters() throws Exception {
        return createParameters();
    }
    @Override
    protected Settings restClientSettings() {
        return Settings.builder()
            .put(super.restClientSettings())
            
            
            
            .put(ESRestTestCase.CLIENT_SOCKET_TIMEOUT, "90s")
            .build();
    }
}