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
assertThat(e.getMessage(), startsWith("index, alias, and data stream names need to be unique"));
    }
    public void testValidateAliasWriteOnly() {
        String alias = randomAlphaOfLength(5);
        String indexA = randomAlphaOfLength(6);
        String indexB = randomAlphaOfLength(7);
        Boolean aWriteIndex = randomBoolean() ? null : randomBoolean();
        Boolean bWriteIndex;
        if (Boolean.TRUE.equals(aWriteIndex)) {
            bWriteIndex = randomFrom(Boolean.FALSE, null);
        } else {
            bWriteIndex = randomFrom(Boolean.TRUE, Boolean.FALSE, null);
        }
        
        Metadata metadata = Metadata.builder().put(buildIndexMetadata(indexA, alias, aWriteIndex)).build();
        
        
        Metadata.builder(metadata).put(buildIndexMetadata(indexB, alias, bWriteIndex)).build();
        
        Exception exception = expectThrows(IllegalStateException.class, () -> {
            IndexMetadata.Builder metaA = buildIndexMetadata(indexA, alias, true);
            IndexMetadata.Builder metaB = buildIndexMetadata(indexB, alias, true);
            Metadata.builder().put(metaA).put(metaB).build();
        });
        assertThat(exception.getMessage(), startsWith("alias [" + alias + "] has more than one write index ["));
    }
    public void testValidateHiddenAliasConsistency() {
        String alias = randomAlphaOfLength(5);
        String indexA = randomAlphaOfLength(6);
        String indexB = randomAlphaOfLength(7);