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/api/grpc/feature/v2/converter.go

@@ -19,6 +19,7 @@ func systemFeaturesToCommand(req *feature_pb.SetSystemFeaturesRequest) *command.
 		ImprovedPerformance:             improvedPerformanceListToDomain(req.ImprovedPerformance),
 		OIDCSingleV1SessionTermination:  req.OidcSingleV1SessionTermination,
 		DisableUserTokenEvent:           req.DisableUserTokenEvent,
+		EnableBackChannelLogout:         req.EnableBackChannelLogout,
 	}
 }
 
@@ -34,6 +35,7 @@ func systemFeaturesToPb(f *query.SystemFeatures) *feature_pb.GetSystemFeaturesRe
 		ImprovedPerformance:                 featureSourceToImprovedPerformanceFlagPb(&f.ImprovedPerformance),
 		OidcSingleV1SessionTermination:      featureSourceToFlagPb(&f.OIDCSingleV1SessionTermination),
 		DisableUserTokenEvent:               featureSourceToFlagPb(&f.DisableUserTokenEvent),
+		EnableBackChannelLogout:             featureSourceToFlagPb(&f.EnableBackChannelLogout),
 	}
 }
 
@@ -50,6 +52,7 @@ func instanceFeaturesToCommand(req *feature_pb.SetInstanceFeaturesRequest) *comm
 		DebugOIDCParentError:            req.DebugOidcParentError,
 		OIDCSingleV1SessionTermination:  req.OidcSingleV1SessionTermination,
 		DisableUserTokenEvent:           req.DisableUserTokenEvent,
+		EnableBackChannelLogout:         req.EnableBackChannelLogout,
 	}
 }
 
@@ -67,6 +70,7 @@ func instanceFeaturesToPb(f *query.InstanceFeatures) *feature_pb.GetInstanceFeat
 		DebugOidcParentError:                featureSourceToFlagPb(&f.DebugOIDCParentError),
 		OidcSingleV1SessionTermination:      featureSourceToFlagPb(&f.OIDCSingleV1SessionTermination),
 		DisableUserTokenEvent:               featureSourceToFlagPb(&f.DisableUserTokenEvent),
+		EnableBackChannelLogout:             featureSourceToFlagPb(&f.EnableBackChannelLogout),
 	}
 }