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
* With this test we ensure that we consider whether a new field added to Metadata should be checked
     * in Metadata.isGlobalStateEquals. We force the instance fields to be either in the checked list
     * or in the excluded list.
     * <p>
     * This prevents from accidentally forgetting that a new field should be checked in isGlobalStateEquals.
     */
    @SuppressForbidden(reason = "need access to all fields, they are mostly private")
    public void testEnsureMetadataFieldCheckedForGlobalStateChanges() {
        Set<String> checkedForGlobalStateChanges = Set.of(
            "coordinationMetadata",
            "persistentSettings",
            "hashesOfConsistentSettings",
            "templates",
            "clusterUUID",
            "clusterUUIDCommitted",
            "customs",
            "reservedStateMetadata"
        );
        Set<String> excludedFromGlobalStateCheck = Set.of(
            "version",
            "transientSettings",
            "settings",
            "indices",
            "aliasedIndices",
            "totalNumberOfShards",
            "totalOpenIndexShards",
            "allIndices",
            "visibleIndices",
            "allOpenIndices",
            "visibleOpenIndices",