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
updated = Set.of(index.getIndex());
            } else {
                final Set<Index> tmp = new HashSet<>(found);
                tmp.add(index.getIndex());
                updated = Set.copyOf(tmp);
            }
            aliasesBuilder.put(alias, updated);
        }
        return aliasesBuilder.build();
    }
    private void ensureNoNameCollision(String indexName) {
        if (indices.containsKey(indexName)) {
            throw new IllegalArgumentException("index with name [" + indexName + "] already exists");
        }
        if (dataStreams().containsKey(indexName)) {
            throw new IllegalArgumentException("data stream with name [" + indexName + "] already exists");
        }
        if (dataStreamAliases().containsKey(indexName)) {
            throw new IllegalStateException("data stream alias and indices alias have the same name (" + indexName + ")");
        }
    }
    public long version() {
        return this.version;
    }
    public String clusterUUID() {
        return this.clusterUUID;
    }
    /**
     * Whether the current node with the given cluster state is locked into the cluster with the UUID returned by {@link #clusterUUID()},
     * meaning that it will not accept any cluster state with a different clusterUUID.