[API] Added terminate_after parameter to Count action

Add `terminate_after` parameter to the Count action to be able to specify
the maximum count for each shard, upon reaching which the query execution
will terminate early.

Also update the link to Elasic Count API guide.

Closes #442

Related: elastic/elasticsearch#26895

Author: dmitry-g

elasticsearch-api/lib/elasticsearch/api/actions/count.rb

@@ -42,7 +42,10 @@ module Actions
       #                                      to a numeric field) should be ignored
       # @option arguments [Boolean] :lowercase_expanded_terms Specify whether query terms should be lowercased
       #
-      # @see http://elasticsearch.org/guide/reference/api/count/
+      # @option arguments [Boolean] :terminate_after Specify the maximum count for each shard, upon reaching
+      #                                              which the query execution will terminate early.
+      #
+      # @see https://www.elastic.co/guide/en/elasticsearch/reference/current/search-count.html
       #
       def count(arguments={})
         valid_params = [
@@ -58,7 +61,8 @@ def count(arguments={})
           :default_operator,
           :df,
           :lenient,
-          :lowercase_expanded_terms ]
+          :lowercase_expanded_terms,
+          :terminate_after ]
 
         method = HTTP_GET
         path   = Utils.__pathify( Utils.__listify(arguments[:index]), Utils.__listify(arguments[:type]), '_count' )