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/integration/instance.go

@@ -49,6 +49,7 @@ const (
 	UserTypeIAMOwner
 	UserTypeOrgOwner
 	UserTypeLogin
+	UserTypeNoPermission
 )
 
 const (
@@ -196,6 +197,7 @@ func (i *Instance) setupInstance(ctx context.Context, token string) {
 	i.createMachineUserInstanceOwner(ctx, token)
 	i.createMachineUserOrgOwner(ctx)
 	i.createLoginClient(ctx)
+	i.createMachineUserNoPermission(ctx)
 	i.createWebAuthNClient()
 }
 
@@ -238,7 +240,17 @@ func (i *Instance) createMachineUserOrgOwner(ctx context.Context) {
 }
 
 func (i *Instance) createLoginClient(ctx context.Context) {
-	i.createMachineUser(ctx, UserTypeLogin)
+	_, err := i.Client.Admin.AddIAMMember(ctx, &admin.AddIAMMemberRequest{
+		UserId: i.createMachineUser(ctx, UserTypeLogin),
+		Roles:  []string{"IAM_LOGIN_CLIENT"},
+	})
+	if err != nil {
+		panic(err)
+	}
+}
+
+func (i *Instance) createMachineUserNoPermission(ctx context.Context) {
+	i.createMachineUser(ctx, UserTypeNoPermission)
 }
 
 func (i *Instance) setClient(ctx context.Context) {