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
imBuilder.putAlias(new AliasMetadata.Builder(newAliasName));
            builder.put(imBuilder);
            imBuilder = new IndexMetadata.Builder(metadata.index("alias-3-2"));
            imBuilder.putAlias(new AliasMetadata.Builder(newAliasName));
            builder.put(imBuilder);
        }
        metadata = builder.build();
        assertThat(metadata.aliasedIndices(), hasSize(numAliases + 1));
        assertThat(
            metadata.aliasedIndices(newAliasName),
            containsInAnyOrder(
                new Index("alias-1-0", ClusterState.UNKNOWN_UUID),
                new Index("alias-2-1", ClusterState.UNKNOWN_UUID),
                new Index("alias-3-2", ClusterState.UNKNOWN_UUID)
            )
        );
        
        builder = Metadata.builder(metadata);
        {
            IndexMetadata.Builder imBuilder = new IndexMetadata.Builder(metadata.index("alias-1-0"));
            imBuilder.removeAlias(newAliasName);
            builder.put(imBuilder);
            imBuilder = new IndexMetadata.Builder(metadata.index("alias-2-1"));
            imBuilder.removeAlias(newAliasName);
            builder.put(imBuilder);
            imBuilder = new IndexMetadata.Builder(metadata.index("alias-3-2"));
            imBuilder.removeAlias(newAliasName);
            builder.put(imBuilder);
        }
        metadata = builder.build();