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
Metadata metadata = builder.build();
            assertThat(previous.getIndicesLookup(), not(sameInstance(metadata.getIndicesLookup())));
            previous = metadata;
        }
        {
            Metadata.Builder builder = Metadata.builder(previous);
            IndexMetadata.Builder imBuilder = IndexMetadata.builder(builder.get(indexName));
            imBuilder.putAlias(AliasMetadata.builder(aliasName).build());
            builder.put(imBuilder);
            Metadata metadata = builder.build();
            assertThat(previous.getIndicesLookup(), not(sameInstance(metadata.getIndicesLookup())));
            previous = metadata;
        }
        {
            Metadata.Builder builder = Metadata.builder(previous);
            IndexMetadata.Builder imBuilder = IndexMetadata.builder(builder.get(indexName));
            imBuilder.putAlias(AliasMetadata.builder(aliasName).writeIndex(true).build());
            builder.put(imBuilder);
            Metadata metadata = builder.build();
            assertThat(previous.getIndicesLookup(), not(sameInstance(metadata.getIndicesLookup())));
            previous = metadata;
        }
        {
            Metadata.Builder builder = Metadata.builder(previous);
            IndexMetadata.Builder imBuilder = IndexMetadata.builder(builder.get(indexName));
            Settings.Builder sBuilder = Settings.builder()
                .put(builder.get(indexName).getSettings())
                .put(IndexMetadata.INDEX_HIDDEN_SETTING.getKey(), true);
            imBuilder.settings(sBuilder.build());
            builder.put(imBuilder);