Deprecate xpack.watcher.history.cleaner_service.enabled

This deprecates the `xpack.watcher.history.cleaner_service.enabled` setting,
since all newly created `.watch-history` indices in 7.0 will use ILM to manage
their retention.

In 8.0 the setting itself and cleanup actions will be removed.

Resolves elastic#32041

docs/reference/monitoring/exporters.asciidoc

@@ -56,15 +56,6 @@ particularly the monitoring indices. To do so, you can take advantage of the
 
 //TO-DO: Add information about index lifecycle management https://github.com/elastic/x-pack-elasticsearch/issues/2814
 
-When using cluster alerts, {watcher} creates daily `.watcher_history*` indices. 
-These are not managed by {monitoring} and they are not curated automatically. It 
-is therefore critical that you curate these indices to avoid an undesirable and 
-unexpected increase in the number of shards and indices and eventually the 
-amount of disk usage. If you are using a `local` exporter, you can set the 
-`xpack.watcher.history.cleaner_service.enabled` setting to `true` and curate the 
-`.watcher_history*` indices by using the 
-<<local-exporter-cleaner,cleaner service>>. See <<general-notification-settings>>. 
-
 There is also a disk watermark (known as the flood stage 
 watermark), which protects clusters from running out of disk space. When this 
 feature is triggered, it makes all indices (including monitoring indices) 

docs/reference/settings/monitoring-settings.asciidoc

@@ -105,11 +105,6 @@ being monitored, and it cannot be disabled.
 
 IMPORTANT: This setting currently only impacts `local`-type exporters. Indices created using
 the `http` exporter will not be deleted automatically.
-
-If both {monitoring} and {watcher} are enabled, you can use this setting to
-affect the {watcher} cleaner service too. For more information, see the
-`xpack.watcher.history.cleaner_service.enabled` setting in the
-<<notification-settings>>.
 --
 
 `xpack.monitoring.exporters`::

docs/reference/settings/notification-settings.asciidoc

@@ -37,6 +37,7 @@ required. For more information, see
 
 `xpack.watcher.history.cleaner_service.enabled`::
 added[6.3.0,Default changed to `true`.]
+deprecated[7.0.0,Watcher history indices are now managed by the `watch-history-ilm-policy` ILM policy]
 +
 Set to `true` (default) to enable the cleaner service. If this setting is
 `true`, the `xpack.monitoring.enabled` setting must also be set to `true` with

x-pack/plugin/monitoring/src/main/java/org/elasticsearch/xpack/monitoring/Monitoring.java

@@ -77,9 +77,9 @@ public class Monitoring extends Plugin implements ActionPlugin {
     /**
      * The ability to automatically cleanup ".watcher_history*" indices while also cleaning up Monitoring indices.
      */
+    @Deprecated
     public static final Setting<Boolean> CLEAN_WATCHER_HISTORY = boolSetting("xpack.watcher.history.cleaner_service.enabled",
-                                                                             true,
-                                                                             Setting.Property.Dynamic, Setting.Property.NodeScope);
+        true, Setting.Property.Dynamic, Setting.Property.NodeScope, Setting.Property.Deprecated);
 
     protected final Settings settings;
     private final boolean enabled;