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/cluster/metadata/Metadata.java
/**
     * Returns the full {@link ReservedStateMetadata} Map for all
     * reserved state namespaces.
     * @return a map of namespace to {@link ReservedStateMetadata}
     */
    public Map<String, ReservedStateMetadata> reservedStateMetadata() {
        return this.reservedStateMetadata;
    }
    /**
     * The collection of index deletions in the cluster.
     */
    public IndexGraveyard indexGraveyard() {
        return custom(IndexGraveyard.TYPE);
    }
    @SuppressWarnings("unchecked")
    public <T extends Custom> T custom(String type) {
        return (T) customs.get(type);
    }
    @SuppressWarnings("unchecked")
    public <T extends Custom> T custom(String type, T defaultValue) {
        return (T) customs.getOrDefault(type, defaultValue);
    }
    /**
     * Gets the total number of shards from all indices, including replicas and
     * closed indices.
     * @return The total number shards from all indices.
     */
    public int getTotalNumberOfShards() {
        return this.totalNumberOfShards;
    }