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

cmd/setup/setup.go

@@ -170,6 +170,7 @@ func Setup(ctx context.Context, config *Config, steps *Steps, masterKey string)
 	steps.s37Apps7OIDConfigsBackChannelLogoutURI = &Apps7OIDConfigsBackChannelLogoutURI{dbClient: esPusherDBClient}
 	steps.s38BackChannelLogoutNotificationStart = &BackChannelLogoutNotificationStart{dbClient: esPusherDBClient, esClient: eventstoreClient}
 	steps.s40InitPushFunc = &InitPushFunc{dbClient: esPusherDBClient}
+	steps.s42Apps7OIDCConfigsLoginVersion = &Apps7OIDCConfigsLoginVersion{dbClient: esPusherDBClient}
 
 	err = projection.Create(ctx, projectionDBClient, eventstoreClient, config.Projections, nil, nil, nil)
 	logging.OnError(err).Fatal("unable to start projections")
@@ -240,6 +241,7 @@ func Setup(ctx context.Context, config *Config, steps *Steps, masterKey string)
 		steps.s32AddAuthSessionID,
 		steps.s33SMSConfigs3TwilioAddVerifyServiceSid,
 		steps.s37Apps7OIDConfigsBackChannelLogoutURI,
+		steps.s42Apps7OIDCConfigsLoginVersion,
 	} {
 		mustExecuteMigration(ctx, eventstoreClient, step, "migration failed")
 	}