Fix ES replicas setting validation

ee/app/models/ee/application_setting.rb

@@ -46,7 +46,7 @@ module EE
 
       validates :elasticsearch_replicas,
                 presence: true,
-                numericality: { only_integer: true, greater_than: 0 }
+                numericality: { only_integer: true, greater_than_or_equal_to: 0 }
 
       validates :elasticsearch_max_bulk_size_mb,
                 presence: true,

ee/spec/models/application_setting_spec.rb

@@ -36,8 +36,8 @@ describe ApplicationSetting do
     it { is_expected.not_to allow_value(-1).for(:elasticsearch_shards) }
 
     it { is_expected.to allow_value(10).for(:elasticsearch_replicas) }
+    it { is_expected.to allow_value(0).for(:elasticsearch_replicas) }
     it { is_expected.not_to allow_value(nil).for(:elasticsearch_replicas) }
-    it { is_expected.not_to allow_value(0).for(:elasticsearch_replicas) }
     it { is_expected.not_to allow_value(1.1).for(:elasticsearch_replicas) }
     it { is_expected.not_to allow_value(-1).for(:elasticsearch_replicas) }