Alerting: Add check for datasource permission in alert rule read API (#47087)

* add check for access to rule's data source in GET APIs

* use more general method GetAlertRules instead of GetNamespaceAlertRules.
* remove unused GetNamespaceAlertRules.

Tests:
* create a method to generate permissions for rules
* extract method to create RuleSrv
* add tests for RouteGetNamespaceRulesConfig

pkg/services/ngalert/api/api.go

@@ -96,7 +96,7 @@ func (api *API) RegisterAPIEndpoints(m *metrics.API) {
 	api.RegisterPrometheusApiEndpoints(NewForkedProm(
 		api.DatasourceCache,
 		NewLotexProm(proxy, logger),
-		&PrometheusSrv{log: logger, manager: api.StateManager, store: api.RuleStore},
+		&PrometheusSrv{log: logger, manager: api.StateManager, store: api.RuleStore, ac: api.AccessControl},
 	), m)
 	// Register endpoints for proxying to Cortex Ruler-compatible backends.
 	api.RegisterRulerApiEndpoints(NewForkedRuler(