Add lower bound on poll_interval (#39593)

A poll_interval of less than 1 second doesn't make much sense,
and can cause  excess load on the master node if 
it's set too low (e.g. single digit milliseconds).

However, we still want to allow relatively short poll intervals,
for testing purposes, so we put a lower limit of 1 second.

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/LifecycleSettings.java

@@ -16,8 +16,8 @@ public class LifecycleSettings {
     public static final String LIFECYCLE_NAME = "index.lifecycle.name";
     public static final String LIFECYCLE_INDEXING_COMPLETE = "index.lifecycle.indexing_complete";
 
-    public static final Setting<TimeValue> LIFECYCLE_POLL_INTERVAL_SETTING = Setting.positiveTimeSetting(LIFECYCLE_POLL_INTERVAL,
-        TimeValue.timeValueMinutes(10), Setting.Property.Dynamic, Setting.Property.NodeScope);
+    public static final Setting<TimeValue> LIFECYCLE_POLL_INTERVAL_SETTING = Setting.timeSetting(LIFECYCLE_POLL_INTERVAL,
+        TimeValue.timeValueMinutes(10), TimeValue.timeValueSeconds(1), Setting.Property.Dynamic, Setting.Property.NodeScope);
     public static final Setting<String> LIFECYCLE_NAME_SETTING = Setting.simpleString(LIFECYCLE_NAME,
         Setting.Property.Dynamic, Setting.Property.IndexScope);
     public static final Setting<Boolean> LIFECYCLE_INDEXING_COMPLETE_SETTING = Setting.boolSetting(LIFECYCLE_INDEXING_COMPLETE, false,