Alerting: Improve validation of query and expressions on rule submit (#53258)

* Improve error messages of server-side expression 
* move validation of alert queries and a condition to eval package

pkg/services/ngalert/api/api.go

@@ -92,6 +92,8 @@ func (api *API) RegisterAPIEndpoints(m *metrics.API) {
 		ac:        api.AccessControl,
 	}
 
+	evaluator := eval.NewEvaluator(api.Cfg, log.New("ngalert.eval"), api.DatasourceCache, api.ExpressionService)
+
 	// Register endpoints for proxying to Alertmanager-compatible backends.
 	api.RegisterAlertmanagerApiEndpoints(NewForkingAM(
 		api.DatasourceCache,
@@ -109,15 +111,15 @@ func (api *API) RegisterAPIEndpoints(m *metrics.API) {
 		api.DatasourceCache,
 		NewLotexRuler(proxy, logger),
 		&RulerSrv{
-			DatasourceCache: api.DatasourceCache,
-			QuotaService:    api.QuotaService,
-			scheduleService: api.Schedule,
-			store:           api.RuleStore,
-			provenanceStore: api.ProvenanceStore,
-			xactManager:     api.TransactionManager,
-			log:             logger,
-			cfg:             &api.Cfg.UnifiedAlerting,
-			ac:              api.AccessControl,
+			conditionValidator: evaluator,
+			QuotaService:       api.QuotaService,
+			scheduleService:    api.Schedule,
+			store:              api.RuleStore,
+			provenanceStore:    api.ProvenanceStore,
+			xactManager:        api.TransactionManager,
+			log:                logger,
+			cfg:                &api.Cfg.UnifiedAlerting,
+			ac:                 api.AccessControl,
 		},
 	), m)
 	api.RegisterTestingApiEndpoints(NewTestingApi(
@@ -126,7 +128,7 @@ func (api *API) RegisterAPIEndpoints(m *metrics.API) {
 			DatasourceCache: api.DatasourceCache,
 			log:             logger,
 			accessControl:   api.AccessControl,
-			evaluator:       eval.NewEvaluator(api.Cfg, log.New("ngalert.eval"), api.DatasourceCache, api.ExpressionService),
+			evaluator:       evaluator,
 		}), m)
 	api.RegisterConfigurationApiEndpoints(NewConfiguration(
 		&ConfigSrv{