Alerting: Implement notification history query endpoint. (#114736)

Implements the /notification/query endpoint on the historian app. Note that it
does not apply any RBAC right now, that will be a follow up commit.

We have to use a go-kit logger in grafana/alerting, so an adapter is needed.
Going from go-kit to slog is a bit hairy but works well enough.

pkg/registry/apps/alerting/historian/register.go

@@ -11,6 +11,7 @@ import (
 	historianAppConfig "github.com/grafana/grafana/apps/alerting/historian/pkg/app/config"
 	"github.com/grafana/grafana/pkg/infra/log"
 	"github.com/grafana/grafana/pkg/services/ngalert"
+	"github.com/grafana/grafana/pkg/services/ngalert/lokiconfig"
 	"github.com/grafana/grafana/pkg/setting"
 )
 
@@ -28,6 +29,24 @@ func RegisterAppInstaller(
 ) (*AlertingHistorianAppInstaller, error) {
 	appSpecificConfig := historianAppConfig.RuntimeConfig{}
 
+	// If we're provided some config, then we can enable some things.
+	if cfg != nil {
+		nhCfg := cfg.UnifiedAlerting.NotificationHistory
+
+		// Only parse config if enabled.
+		if nhCfg.Enabled {
+			lokiConfig, err := lokiconfig.NewLokiConfig(cfg.UnifiedAlerting.NotificationHistory.LokiSettings)
+			if err != nil {
+				return nil, err
+			}
+
+			appSpecificConfig.Notification = historianAppConfig.NotificationConfig{
+				Enabled: nhCfg.Enabled,
+				Loki:    lokiConfig,
+			}
+		}
+	}
+
 	// If we're provided an AlertNG, then call back into that for things we need.
 	// This is a temporary whilst building out the app; we should not depend on it.
 	if ng != nil {