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
int size = in.readVInt();
        for (int i = 0; i < size; i++) {
            builder.put(IndexMetadata.readFrom(in, mappingLookup), false);
        }
        size = in.readVInt();
        for (int i = 0; i < size; i++) {
            builder.put(IndexTemplateMetadata.readFrom(in));
        }
        int customSize = in.readVInt();
        for (int i = 0; i < customSize; i++) {
            Custom customIndexMetadata = in.readNamedWriteable(Custom.class);
            builder.putCustom(customIndexMetadata.getWriteableName(), customIndexMetadata);
        }
        if (in.getTransportVersion().onOrAfter(TransportVersion.V_8_4_0)) {
            int reservedStateSize = in.readVInt();
            for (int i = 0; i < reservedStateSize; i++) {
                builder.put(ReservedStateMetadata.readFrom(in));
            }
        }
        return builder.build();
    }
    @Override
    public void writeTo(StreamOutput out) throws IOException {
        out.writeLong(version);
        out.writeString(clusterUUID);
        out.writeBoolean(clusterUUIDCommitted);
        coordinationMetadata.writeTo(out);
        transientSettings.writeTo(out);
        persistentSettings.writeTo(out);
        if (out.getTransportVersion().onOrAfter(TransportVersion.V_7_3_0)) {