feat: Feature flag for relational tables (#10599)

# Which Problems Are Solved

This PR introduces a new feature flag `EnableRelationalTables` that will
be used in following implementations to decide whether Zitadel should
use the relational model or the event sourcing one.

# TODO

  - [x] Implement flag at system level
- [x] Display the flag on console:
https://github.com/zitadel/zitadel/pull/10615

# How the Problems Are Solved

  - Implement loading the flag from config
- Add persistence of the flag through gRPC endpoint
(SetInstanceFeatures)
- Implement reading of the flag through gRPC endpoint
(GetInstanceFeatures)

# Additional Changes

Some minor refactoring to remove un-needed generics annotations

# Additional Context

- Closes #10574

---------

Co-authored-by: Silvan <[email protected]>

internal/query/instance_features.go

@@ -19,6 +19,7 @@ type InstanceFeatures struct {
 	LoginV2                        FeatureSource[*feature.LoginV2]
 	PermissionCheckV2              FeatureSource[bool]
 	ConsoleUseV2UserApi            FeatureSource[bool]
+	EnableRelationalTables         FeatureSource[bool]
 }
 
 func (q *Queries) GetInstanceFeatures(ctx context.Context, cascade bool) (_ *InstanceFeatures, err error) {

internal/query/instance_features_model.go

@@ -72,11 +72,13 @@ func (m *InstanceFeaturesReadModel) Query() *eventstore.SearchQueryBuilder {
 			feature_v2.InstanceLoginVersion,
 			feature_v2.InstancePermissionCheckV2,
 			feature_v2.InstanceConsoleUseV2UserApi,
+			feature_v2.InstanceEnableRelationalTables,
 		).
 		Builder().ResourceOwner(m.ResourceOwner)
 }
 
 func (m *InstanceFeaturesReadModel) reduceReset() {
+	m.instance.EnableRelationalTables = FeatureSource[bool]{}
 	if m.populateFromSystem() {
 		return
 	}
@@ -126,6 +128,8 @@ func reduceInstanceFeatureSet[T any](features *InstanceFeatures, event *feature_
 		features.PermissionCheckV2.set(level, event.Value)
 	case feature.KeyConsoleUseV2UserApi:
 		features.ConsoleUseV2UserApi.set(level, event.Value)
+	case feature.KeyEnableRelationalTables:
+		features.EnableRelationalTables.set(level, event.Value)
 	}
 	return nil
 }

internal/query/projection/instance_features.go

@@ -104,6 +104,10 @@ func (*instanceFeatureProjection) Reducers() []handler.AggregateReducer {
 				Event:  instance.InstanceRemovedEventType,
 				Reduce: reduceInstanceRemovedHelper(InstanceDomainInstanceIDCol),
 			},
+			{
+				Event:  feature_v2.InstanceEnableRelationalTables,
+				Reduce: reduceInstanceSetFeature[bool],
+			},
 		},
 	}}
 }

internal/query/system_features.go

@@ -28,6 +28,7 @@ type SystemFeatures struct {
 	EnableBackChannelLogout        FeatureSource[bool]
 	LoginV2                        FeatureSource[*feature.LoginV2]
 	PermissionCheckV2              FeatureSource[bool]
+	EnableRelationalTables         FeatureSource[bool]
 }
 
 func (q *Queries) GetSystemFeatures(ctx context.Context) (_ *SystemFeatures, err error) {

internal/query/system_features_model.go

@@ -63,6 +63,7 @@ func (m *SystemFeaturesReadModel) Query() *eventstore.SearchQueryBuilder {
 			feature_v2.SystemEnableBackChannelLogout,
 			feature_v2.SystemLoginVersion,
 			feature_v2.SystemPermissionCheckV2,
+			feature_v2.SystemEnableRelationalTables,
 		).
 		Builder().ResourceOwner(m.ResourceOwner)
 }
@@ -96,6 +97,8 @@ func reduceSystemFeatureSet[T any](features *SystemFeatures, event *feature_v2.S
 		features.LoginV2.set(level, event.Value)
 	case feature.KeyPermissionCheckV2:
 		features.PermissionCheckV2.set(level, event.Value)
+	case feature.KeyEnableRelationalTables:
+		features.EnableRelationalTables.set(level, event.Value)
 	}
 	return nil
 }

internal/query/system_features_test.go

@@ -53,6 +53,10 @@ func TestQueries_GetSystemFeatures(t *testing.T) {
 						context.Background(), aggregate,
 						feature_v2.SystemUserSchemaEventType, false,
 					)),
+					eventFromEventPusher(feature_v2.NewSetEvent(
+						context.Background(), aggregate,
+						feature_v2.SystemEnableRelationalTables, false,
+					)),
 				),
 			),
 			want: &SystemFeatures{
@@ -67,6 +71,10 @@ func TestQueries_GetSystemFeatures(t *testing.T) {
 					Level: feature.LevelSystem,
 					Value: false,
 				},
+				EnableRelationalTables: FeatureSource[bool]{
+					Level: feature.LevelSystem,
+					Value: false,
+				},
 			},
 		},
 		{