TSDB: fix error without feature flag (elastic#80945)

When you haven't enable the tsdb feature flag we would refuse to start.
That's bad because we will likely release with the feature flag
disabled. This should get us starting again. It fixes:

* We tried to register a settings update consumer for the `end_time` for
  the tsdb index even when the `end_time` setting wasn't registered.
* Pass the tsdb feature flag to internal cluster tests.

Author: nik9000

server/build.gradle

@@ -132,6 +132,9 @@ if (BuildParams.isSnapshotBuild() == false) {
     tasks.named("test").configure {
         systemProperty 'es.index_mode_feature_flag_registered', 'true'
     }
+    tasks.named("internalClusterTest").configure {
+        systemProperty 'es.index_mode_feature_flag_registered', 'true'
+    }
 }
 
 tasks.named("thirdPartyAudit").configure {

server/src/main/java/org/elasticsearch/index/IndexSettings.java

@@ -813,7 +813,9 @@ public IndexSettings(final IndexMetadata indexMetadata, final Settings nodeSetti
         scopedSettings.addSettingsUpdateConsumer(INDEX_MAPPING_DEPTH_LIMIT_SETTING, this::setMappingDepthLimit);
         scopedSettings.addSettingsUpdateConsumer(INDEX_MAPPING_FIELD_NAME_LENGTH_LIMIT_SETTING, this::setMappingFieldNameLengthLimit);
         scopedSettings.addSettingsUpdateConsumer(INDEX_MAPPING_DIMENSION_FIELDS_LIMIT_SETTING, this::setMappingDimensionFieldsLimit);
-        scopedSettings.addSettingsUpdateConsumer(TIME_SERIES_END_TIME, this::updateTimeSeriesEndTime);
+        if (IndexSettings.isTimeSeriesModeEnabled()) {
+            scopedSettings.addSettingsUpdateConsumer(TIME_SERIES_END_TIME, this::updateTimeSeriesEndTime);
+        }
     }
 
     private void setSearchIdleAfter(TimeValue searchIdleAfter) {