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/command/project_application_oidc.go

@@ -32,6 +32,8 @@ type addOIDCApp struct {
 	AdditionalOrigins           []string
 	SkipSuccessPageForNativeApp bool
 	BackChannelLogoutURI        string
+	LoginVersion                domain.LoginVersion
+	LoginBaseURI                string
 
 	ClientID          string
 	ClientSecret      string
@@ -110,6 +112,8 @@ func (c *Commands) AddOIDCAppCommand(app *addOIDCApp) preparation.Validation {
 					trimStringSliceWhiteSpaces(app.AdditionalOrigins),
 					app.SkipSuccessPageForNativeApp,
 					app.BackChannelLogoutURI,
+					app.LoginVersion,
+					app.LoginBaseURI,
 				),
 			}, nil
 		}, nil
@@ -202,6 +206,8 @@ func (c *Commands) addOIDCApplicationWithID(ctx context.Context, oidcApp *domain
 		trimStringSliceWhiteSpaces(oidcApp.AdditionalOrigins),
 		oidcApp.SkipNativeAppSuccessPage,
 		strings.TrimSpace(oidcApp.BackChannelLogoutURI),
+		oidcApp.LoginVersion,
+		strings.TrimSpace(oidcApp.LoginBaseURI),
 	))
 
 	addedApplication.AppID = oidcApp.AppID
@@ -260,6 +266,8 @@ func (c *Commands) ChangeOIDCApplication(ctx context.Context, oidc *domain.OIDCA
 		trimStringSliceWhiteSpaces(oidc.AdditionalOrigins),
 		oidc.SkipNativeAppSuccessPage,
 		strings.TrimSpace(oidc.BackChannelLogoutURI),
+		oidc.LoginVersion,
+		strings.TrimSpace(oidc.LoginBaseURI),
 	)
 	if err != nil {
 		return nil, err