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.
server/src/main/java/org/elasticsearch/action/admin/indices/rollover/MetadataRolloverService.java
public String toString() {
            return String.format(
                Locale.ROOT,
                "cluster state version [%d], rollover index name [%s], source index name [%s]",
                clusterState.version(),
                rolloverIndexName,
                sourceIndexName
            );
        }
    }
    public RolloverResult rolloverClusterState(
        ClusterState currentState,
        String rolloverTarget,
        String newIndexName,
        CreateIndexRequest createIndexRequest,
        List<Condition<?>> metConditions,
        Instant now,
        boolean silent,
        boolean onlyValidate,
        @Nullable IndexMetadataStats sourceIndexStats
    ) throws Exception {
        validate(currentState.metadata(), rolloverTarget, newIndexName, createIndexRequest);
        final IndexAbstraction indexAbstraction = currentState.metadata().getIndicesLookup().get(rolloverTarget);
        return switch (indexAbstraction.getType()) {
            case ALIAS -> rolloverAlias(
                currentState,
                (IndexAbstraction.Alias) indexAbstraction,
                rolloverTarget,
                newIndexName,
                createIndexRequest,