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
Map<String, Object> map = (Map<String, Object>) value;
                    Map<String, Object> subFields = (Map<String, Object>) map.get("fields");
                    assert subFields.size() > 0;
                    map.put("properties", subFields);
                    map.remove("fields");
                    map.remove("type");
                }
            }
        }
        
        return fields.size() == 0;
    }
    private static String mergePaths(String path, String field) {
        if (path.length() == 0) {
            return field;
        }
        return path + "." + field;
    }
    /**
     * Returns all the concrete indices.
     */
    public String[] getConcreteAllIndices() {
        return allIndices;
    }
    /**
     * Returns all the concrete indices that are not hidden.
     */
    public String[] getConcreteVisibleIndices() {
        return visibleIndices;
    }