Point deprecated settings to the new location. (#10522)

I was looking through some cluster settings, stumbled across the search
back-pressure settings, saw they were deprecated, and the Javadoc
alluded to some myserious new settings.

I'm adding links to the class with the new settings to help future
developers.

Signed-off-by: Michael Froh <froh@amazon.com>

server/src/main/java/org/opensearch/search/backpressure/settings/SearchBackpressureSettings.java

@@ -55,7 +55,7 @@ private static class Defaults {
      * Defines the percentage of tasks to cancel relative to the number of successful task completions.
      * In other words, it is the number of tokens added to the bucket on each successful task completion.
      * <p>
-     * The setting below is deprecated.
+     * The setting below is deprecated. The new setting is in {@link SearchShardTaskSettings}.
      * To keep backwards compatibility, the old usage is remained, and it's also used as the fallback for the new usage.
      */
     public static final Setting<Double> SETTING_CANCELLATION_RATIO = Setting.doubleSetting(
@@ -72,7 +72,7 @@ private static class Defaults {
      * Defines the number of tasks to cancel per unit time (in millis).
      * In other words, it is the number of tokens added to the bucket each millisecond.
      * <p>
-     * The setting below is deprecated.
+     * The setting below is deprecated. The new setting is in {@link SearchShardTaskSettings}.
      * To keep backwards compatibility, the old usage is remained, and it's also used as the fallback for the new usage.
      */
     public static final Setting<Double> SETTING_CANCELLATION_RATE = Setting.doubleSetting(
@@ -87,7 +87,7 @@ private static class Defaults {
     /**
      * Defines the maximum number of tasks that can be cancelled before being rate-limited.
      * <p>
-     * The setting below is deprecated.
+     * The setting below is deprecated. The new setting is in {@link SearchShardTaskSettings}.
      * To keep backwards compatibility, the old usage is remained, and it's also used as the fallback for the new usage.
      */
     public static final Setting<Double> SETTING_CANCELLATION_BURST = Setting.doubleSetting(