Alerting: Make context deadline on AlertNG service startup configurable (#96053)

* Make alerting context deadline configurable

* Remove debug logs

* Change default timeout

* Update tests

pkg/services/cloudmigration/cloudmigrationimpl/cloudmigration_test.go

@@ -790,6 +790,7 @@ func setUpServiceTest(t *testing.T, withDashboardMock bool) cloudmigration.Servi
 
 	cfg.UnifiedAlerting.DefaultRuleEvaluationInterval = time.Minute
 	cfg.UnifiedAlerting.BaseInterval = time.Minute
+	cfg.UnifiedAlerting.InitializationTimeout = 30 * time.Second
 	ruleStore, err := ngalertstore.ProvideDBStore(cfg, featureToggles, sqlStore, mockFolder, dashboardService, fakeAccessControl, bus)
 	require.NoError(t, err)