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
builder.put(IndexTemplateMetadata.Builder.fromXContent(parser, parser.currentName()));
                        }
                    } else if ("reserved_state".equals(currentFieldName)) {
                        while ((token = parser.nextToken()) != XContentParser.Token.END_OBJECT) {
                            builder.put(ReservedStateMetadata.fromXContent(parser));
                        }
                    } else {
                        try {
                            Custom custom = parser.namedObject(Custom.class, currentFieldName, null);
                            builder.putCustom(custom.getWriteableName(), custom);
                        } catch (NamedObjectNotFoundException ex) {
                            logger.warn("Skipping unknown custom object with type {}", currentFieldName);
                            parser.skipChildren();
                        }
                    }
                } else if (token.isValue()) {
                    if ("version".equals(currentFieldName)) {
                        builder.version = parser.longValue();
                    } else if ("cluster_uuid".equals(currentFieldName) || "uuid".equals(currentFieldName)) {
                        builder.clusterUUID = parser.text();
                    } else if ("cluster_uuid_committed".equals(currentFieldName)) {
                        builder.clusterUUIDCommitted = parser.booleanValue();
                    } else {
                        throw new IllegalArgumentException("Unexpected field [" + currentFieldName + "]");
                    }
                } else {
                    throw new IllegalArgumentException("Unexpected token " + token);
                }
            }
            XContentParserUtils.ensureExpectedToken(XContentParser.Token.END_OBJECT, parser.nextToken(), parser);