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/admin/import.go

@@ -644,7 +644,15 @@ func importOIDCApps(ctx context.Context, s *Server, errors *[]*admin_pb.ImportDa
 	}
 	for _, app := range org.GetOidcApps() {
 		logging.Debugf("import oidcapplication: %s", app.GetAppId())
-		_, err := s.command.AddOIDCApplicationWithID(ctx, management.AddOIDCAppRequestToDomain(app.App), org.GetOrgId(), app.GetAppId())
+		oidcApp, err := management.AddOIDCAppRequestToDomain(app.App)
+		if err != nil {
+			*errors = append(*errors, &admin_pb.ImportDataError{Type: "oidc_app", Id: app.GetAppId(), Message: err.Error()})
+			if isCtxTimeout(ctx) {
+				return err
+			}
+			continue
+		}
+		_, err = s.command.AddOIDCApplicationWithID(ctx, oidcApp, org.GetOrgId(), app.GetAppId())
 		if err != nil {
 			*errors = append(*errors, &admin_pb.ImportDataError{Type: "oidc_app", Id: app.GetAppId(), Message: err.Error()})
 			if isCtxTimeout(ctx) {

internal/api/grpc/admin/integration_test/iam_member_test.go

@@ -25,6 +25,7 @@ var iamRoles = []string{
 	"IAM_USER_MANAGER",
 	"IAM_ADMIN_IMPERSONATOR",
 	"IAM_END_USER_IMPERSONATOR",
+	"IAM_LOGIN_CLIENT",
 }
 
 func TestServer_ListIAMMemberRoles(t *testing.T) {