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
indicesMap,
            updatedAliases,
            templates,
            customs,
            updatedAllIndices,
            updatedVisibleIndices,
            updatedOpenIndices,
            updatedVisibleOpenIndices,
            updatedClosedIndices,
            updatedVisibleClosedIndices,
            null,
            updatedMappingsByHash,
            IndexVersion.min(index.getCompatibilityVersion(), oldestIndexVersion),
            reservedStateMetadata
        );
    }
    private ImmutableOpenMap<String, Set<Index>> aliasesAfterAddingIndex(IndexMetadata index, Map<String, AliasMetadata> aliases) {
        if (aliases.isEmpty()) {
            return aliasedIndices;
        }
        final String indexName = index.getIndex().getName();
        final ImmutableOpenMap.Builder<String, Set<Index>> aliasesBuilder = ImmutableOpenMap.builder(aliasedIndices);
        for (String alias : aliases.keySet()) {
            ensureNoNameCollision(alias);
            if (aliasedIndices.containsKey(indexName)) {
                throw new IllegalArgumentException("alias with name [" + indexName + "] already exists");
            }
            final Set<Index> found = aliasesBuilder.get(alias);
            final Set<Index> updated;
            if (found == null) {