Alerting: Refactor Evaluator (#51673)

* AlertRule to return condition
* update ConditionEval to not return an error because it's always nil
* make getExprRequest private
* refactor executeCondition to just converter and move execution to the ConditionEval as this makes code more readable.
* log error if results have errors
* change signature of evaluate function to not return an error

pkg/services/ngalert/api/api_testing.go

@@ -55,10 +55,7 @@ func (srv TestingApiSrv) RouteTestGrafanaRuleConfig(c *models.ReqContext, body a
 		now = timeNow()
 	}
 
-	evalResults, err := srv.evaluator.ConditionEval(&evalCond, now)
-	if err != nil {
-		return ErrResp(http.StatusBadRequest, err, "Failed to evaluate conditions")
-	}
+	evalResults := srv.evaluator.ConditionEval(evalCond, now)
 
 	frame := evalResults.AsDataFrame()
 	return response.JSONStreaming(http.StatusOK, util.DynMap{