Alerting: Introduce proper feature toggles for common state history backend combinations (#65497)

* define 3 feature toggles for rollout phases

* Pass feature toggles along

* Implement first feature toggle

* Try a different strategy with fall-throughs to specific configurations

* Apply toggle overrides once outside of backend composition

* Emit log messages when we coerce backends

* Run code generator for feature toggle files

* Improve wording in flag descs

* Re-run generator

* Use code-generated constants instead of plain strings

* Use converted enum values rather than strings for pre-parsing

pkg/services/featuremgmt/registry.go

@@ -461,5 +461,23 @@ var (
 			State:       FeatureStateAlpha,
 			Owner:       grafanaObservabilityMetricsSquad,
 		},
+		{
+			Name:        "alertStateHistoryLokiSecondary",
+			Description: "Enable Grafana to write alert state history to an external Loki instance in addition to Grafana annotations.",
+			State:       FeatureStateAlpha,
+			Owner:       grafanaAlertingSquad,
+		},
+		{
+			Name:        "alertStateHistoryLokiPrimary",
+			Description: "Enable a remote Loki instance as the primary source for state history reads.",
+			State:       FeatureStateAlpha,
+			Owner:       grafanaAlertingSquad,
+		},
+		{
+			Name:        "alertStateHistoryLokiOnly",
+			Description: "Disable Grafana alerts from emitting annotations when a remote Loki instance is available.",
+			State:       FeatureStateAlpha,
+			Owner:       grafanaAlertingSquad,
+		},
 	}
 )