feat(OIDC): add back channel logout (#8837)

# Which Problems Are Solved

Currently ZITADEL supports RP-initiated logout for clients. Back-channel
logout ensures that user sessions are terminated across all connected
applications, even if the user closes their browser or loses
connectivity providing a more secure alternative for certain use cases.

# How the Problems Are Solved

If the feature is activated and the client used for the authentication
has a back_channel_logout_uri configured, a
`session_logout.back_channel` will be registered. Once a user terminates
their session, a (notification) handler will send a SET (form POST) to
the registered uri containing a logout_token (with the user's ID and
session ID).

- A new feature "back_channel_logout" is added on system and instance
level
- A `back_channel_logout_uri` can be managed on OIDC applications
- Added a `session_logout` aggregate to register and inform about sent
`back_channel` notifications
- Added a `SecurityEventToken` channel and `Form`message type in the
notification handlers
- Added `TriggeredAtOrigin` fields to `HumanSignedOut` and
`TerminateSession` events for notification handling
- Exported various functions and types in the `oidc` package to be able
to reuse for token signing in the back_channel notifier.
- To prevent that current existing session termination events will be
handled, a setup step is added to set the `current_states` for the
`projections.notifications_back_channel_logout` to the current position

- [x] requires https://github.com/zitadel/oidc/pull/671

# Additional Changes

- Updated all OTEL dependencies to v1.29.0, since OIDC already updated
some of them to that version.
- Single Session Termination feature is correctly checked (fixed feature
mapping)

# Additional Context

- closes https://github.com/zitadel/zitadel/issues/8467
- TODO:
  - Documentation
  - UI to be done: https://github.com/zitadel/zitadel/issues/8469

---------

Co-authored-by: Hidde Wieringa <hidde@hiddewieringa.nl>

internal/command/system_features_model.go

@@ -62,6 +62,7 @@ func (m *SystemFeaturesWriteModel) Query() *eventstore.SearchQueryBuilder {
 			feature_v2.SystemImprovedPerformanceEventType,
 			feature_v2.SystemOIDCSingleV1SessionTerminationEventType,
 			feature_v2.SystemDisableUserTokenEvent,
+			feature_v2.SystemEnableBackChannelLogout,
 		).
 		Builder().ResourceOwner(m.ResourceOwner)
 }
@@ -100,6 +101,9 @@ func reduceSystemFeature(features *SystemFeatures, key feature.Key, value any) {
 	case feature.KeyDisableUserTokenEvent:
 		v := value.(bool)
 		features.DisableUserTokenEvent = &v
+	case feature.KeyEnableBackChannelLogout:
+		v := value.(bool)
+		features.EnableBackChannelLogout = &v
 	}
 }
 
@@ -115,6 +119,7 @@ func (wm *SystemFeaturesWriteModel) setCommands(ctx context.Context, f *SystemFe
 	cmds = appendFeatureSliceUpdate(ctx, cmds, aggregate, wm.ImprovedPerformance, f.ImprovedPerformance, feature_v2.SystemImprovedPerformanceEventType)
 	cmds = appendFeatureUpdate(ctx, cmds, aggregate, wm.OIDCSingleV1SessionTermination, f.OIDCSingleV1SessionTermination, feature_v2.SystemOIDCSingleV1SessionTerminationEventType)
 	cmds = appendFeatureUpdate(ctx, cmds, aggregate, wm.DisableUserTokenEvent, f.DisableUserTokenEvent, feature_v2.SystemDisableUserTokenEvent)
+	cmds = appendFeatureUpdate(ctx, cmds, aggregate, wm.EnableBackChannelLogout, f.EnableBackChannelLogout, feature_v2.SystemEnableBackChannelLogout)
 	return cmds
 }