fix: Muting rule inter condition operator ambiguous

Author: bdanek-ert

newrelic/resource_newrelic_alert_muting_rule.go

@@ -157,6 +157,7 @@ func resourceNewRelicAlertMutingRule() *schema.Resource {
 							Type:        schema.TypeString,
 							Required:    true,
 							Description: "The operator used to combine all the MutingRuleConditions within the group.",
+							ValidateFunc: validation.StringInSlice([]string{"AND", "OR"}, true),
 						},
 					},
 				},

website/docs/r/alert_muting_rule.html.markdown

@@ -60,7 +60,7 @@ The following arguments are supported:
 
 All nested `condition` blocks support the following arguments:
   * `conditions` - (Optional) The individual MutingRuleConditions within the group. See [Nested conditions blocks](#nested-conditions-blocks) below for details.
-  * `operator` - (Required) The operator used to combine all the MutingRuleConditions within the group.
+  * `operator` - (Required) The operator used to combine all the MutingRuleConditions within the group. Valid values are `AND`, `OR`. 
 
 
 ### Nested `conditions` blocks