Alerting: Condition evaluator with cached pipeline (#57479)

* create rule evaluator
* load header from the context
* init one factory
* update scheduler

pkg/tests/api/alerting/api_alertmanager_test.go

@@ -2483,7 +2483,7 @@ func TestEval(t *testing.T) {
 				if setting.IsEnterprise {
 					return "user is not authorized to query one or many data sources used by the rule"
 				}
-				return "Failed to evaluate queries and expressions: failed to execute conditions: failed to build query 'A': data source not found"
+				return "Failed to build evaluator for queries and expressions: failed to build query 'A': data source not found"
 			},
 		},
 	}