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
aliasedIndices,
            templates,
            customs,
            allIndices,
            visibleIndices,
            allOpenIndices,
            visibleOpenIndices,
            allClosedIndices,
            visibleClosedIndices,
            indicesLookup,
            mappingsByHash,
            oldestIndexVersion,
            reservedStateMetadata
        );
    }
    /**
     * Creates a copy of this instance with the given {@code index} added.
     * @param index index to add
     * @return copy with added index
     */
    public Metadata withAddedIndex(IndexMetadata index) {
        final String indexName = index.getIndex().getName();
        ensureNoNameCollision(indexName);
        final Map<String, AliasMetadata> aliases = index.getAliases();
        final ImmutableOpenMap<String, Set<Index>> updatedAliases = aliasesAfterAddingIndex(index, aliases);
        final String[] updatedVisibleIndices;
        if (index.isHidden()) {
            updatedVisibleIndices = visibleIndices;
        } else {
            updatedVisibleIndices = ArrayUtils.append(visibleIndices, indexName);