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(aliases, anEmptyMap());
        }
        {
            final GetAliasesRequest request;
            if (randomBoolean()) {
                request = new GetAliasesRequest();
            } else {
                request = new GetAliasesRequest(randomFrom("alias1", "alias2"));
                
                request.replaceAliases(Strings.EMPTY_ARRAY);
            }
            Map<String, List<AliasMetadata>> aliases = metadata.findAliases(request.aliases(), new String[] { "index" });
            assertThat(aliases, aMapWithSize(1));
            List<AliasMetadata> aliasMetadataList = aliases.get("index");
            assertThat(aliasMetadataList, transformedItemsMatch(AliasMetadata::alias, contains("alias1", "alias2")));
        }
        {
            GetAliasesRequest request = new GetAliasesRequest("alias*");
            Map<String, List<AliasMetadata>> aliases = metadata.findAliases(request.aliases(), new String[] { "index" });
            assertThat(aliases, aMapWithSize(1));
            List<AliasMetadata> aliasMetadataList = aliases.get("index");
            assertThat(aliasMetadataList, transformedItemsMatch(AliasMetadata::alias, contains("alias1", "alias2")));
        }
        {
            GetAliasesRequest request = new GetAliasesRequest("alias1");
            Map<String, List<AliasMetadata>> aliases = metadata.findAliases(request.aliases(), new String[] { "index" });
            assertThat(aliases, aMapWithSize(1));
            List<AliasMetadata> aliasMetadataList = aliases.get("index");
            assertThat(aliasMetadataList, transformedItemsMatch(AliasMetadata::alias, contains("alias1")));
        }