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/test/java/org/elasticsearch/cluster/metadata/MetadataTests.java
for (int i = 0; i < indexCount; i++) {
            indices.add(randomAlphaOfLength(10));
        }
        Map<String, Set<String>> aliasToIndices = new HashMap<>();
        for (String alias : randomSubsetOf(randomIntBetween(1, 10), indices)) {
            Set<String> indicesInAlias;
            do {
                indicesInAlias = new HashSet<>(randomSubsetOf(randomIntBetween(1, 3), indices));
                indicesInAlias.remove(alias);
            } while (indicesInAlias.isEmpty());
            aliasToIndices.put(alias, indicesInAlias);
        }
        int properAliases = randomIntBetween(0, 3);
        for (int i = 0; i < properAliases; i++) {
            aliasToIndices.put(randomAlphaOfLength(5), new HashSet<>(randomSubsetOf(randomIntBetween(1, 3), indices)));
        }
        Metadata.Builder metadataBuilder = Metadata.builder();
        for (String index : indices) {
            IndexMetadata.Builder indexBuilder = IndexMetadata.builder(index)
                .settings(Settings.builder().put(IndexMetadata.SETTING_VERSION_CREATED, IndexVersion.current()))
                .numberOfShards(1)
                .numberOfReplicas(0);
            aliasToIndices.forEach((key, value) -> {
                if (value.contains(index)) {
                    indexBuilder.putAlias(AliasMetadata.builder(key).build());
                }
            });
            metadataBuilder.put(indexBuilder);
        }
        Exception e = expectThrows(IllegalStateException.class, metadataBuilder::build);