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
Iterator<Map.Entry<String, Object>> entryIterator = fields.entrySet().iterator();
        while (entryIterator.hasNext()) {
            Map.Entry<String, Object> entry = entryIterator.next();
            String newPath = mergePaths(currentPath, entry.getKey());
            Object value = entry.getValue();
            boolean mayRemove = true;
            boolean isMultiField = false;
            if (value instanceof Map) {
                Map<String, Object> map = (Map<String, Object>) value;
                Map<String, Object> properties = (Map<String, Object>) map.get("properties");
                if (properties != null) {
                    mayRemove = filterFields(newPath, properties, fieldPredicate);
                } else {
                    Map<String, Object> subFields = (Map<String, Object>) map.get("fields");
                    if (subFields != null) {
                        isMultiField = true;
                        if (mayRemove = filterFields(newPath, subFields, fieldPredicate)) {
                            map.remove("fields");
                        }
                    }
                }
            } else {
                throw new IllegalStateException("cannot filter mappings, found unknown element of type [" + value.getClass() + "]");
            }
            
            if (fieldPredicate.test(newPath) == false) {
                if (mayRemove) {
                    entryIterator.remove();
                } else if (isMultiField) {