feat: specify login UI version on instance and apps (#9071)

# Which Problems Are Solved

To be able to migrate or test the new login UI, admins might want to
(temporarily) switch individual apps.
At a later point admin might want to make sure all applications use the
new login UI.

# How the Problems Are Solved

- Added a feature flag `` on instance level to require all apps to use
the new login and provide an optional base url.
- if the flag is enabled, all (OIDC) applications will automatically use
the v2 login.
  - if disabled, applications can decide based on their configuration
- Added an option on OIDC apps to use the new login UI and an optional
base url.
- Removed the requirement to use `x-zitadel-login-client` to be
redirected to the login V2 and retrieve created authrequest and link
them to SSO sessions.
- Added a new "IAM_LOGIN_CLIENT" role to allow management of users,
sessions, grants and more without `x-zitadel-login-client`.

# Additional Changes

None

# Additional Context

closes https://github.com/zitadel/zitadel/issues/8702

internal/api/grpc/management/project_application.go

@@ -80,7 +80,11 @@ func (s *Server) ListAppChanges(ctx context.Context, req *mgmt_pb.ListAppChanges
 }
 
 func (s *Server) AddOIDCApp(ctx context.Context, req *mgmt_pb.AddOIDCAppRequest) (*mgmt_pb.AddOIDCAppResponse, error) {
-	app, err := s.command.AddOIDCApplication(ctx, AddOIDCAppRequestToDomain(req), authz.GetCtxData(ctx).OrgID)
+	oidcApp, err := AddOIDCAppRequestToDomain(req)
+	if err != nil {
+		return nil, err
+	}
+	app, err := s.command.AddOIDCApplication(ctx, oidcApp, authz.GetCtxData(ctx).OrgID)
 	if err != nil {
 		return nil, err
 	}
@@ -128,7 +132,11 @@ func (s *Server) UpdateApp(ctx context.Context, req *mgmt_pb.UpdateAppRequest) (
 }
 
 func (s *Server) UpdateOIDCAppConfig(ctx context.Context, req *mgmt_pb.UpdateOIDCAppConfigRequest) (*mgmt_pb.UpdateOIDCAppConfigResponse, error) {
-	config, err := s.command.ChangeOIDCApplication(ctx, UpdateOIDCAppConfigRequestToDomain(req), authz.GetCtxData(ctx).OrgID)
+	oidcApp, err := UpdateOIDCAppConfigRequestToDomain(req)
+	if err != nil {
+		return nil, err
+	}
+	config, err := s.command.ChangeOIDCApplication(ctx, oidcApp, authz.GetCtxData(ctx).OrgID)
 	if err != nil {
 		return nil, err
 	}