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/instance_test.go

@@ -128,6 +128,8 @@ func oidcAppEvents(ctx context.Context, orgID, projectID, id, name, clientID str
 			nil,
 			false,
 			"",
+			domain.LoginVersionUnspecified,
+			"",
 		),
 	}
 }
@@ -441,6 +443,8 @@ func generatedDomainFilters(instanceID, orgID, projectID, appID, generatedDomain
 				nil,
 				false,
 				"",
+				domain.LoginVersionUnspecified,
+				"",
 			),
 		),
 		expectFilter(