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/defaults.yaml

@@ -1289,6 +1289,7 @@ InternalAuthZ:
         - "project.grant.member.delete"
         - "events.read"
         - "milestones.read"
+        - "session.read"
         - "session.delete"
         - "action.target.read"
         - "action.target.write"
@@ -1481,6 +1482,43 @@ InternalAuthZ:
         - "project.grant.member.write"
         - "project.grant.member.delete"
         - "session.delete"
+    - Role: "IAM_LOGIN_CLIENT"
+      Permissions:
+        - "iam.read"
+        - "iam.policy.read"
+        - "iam.member.read"
+        - "iam.member.write"
+        - "iam.idp.read"
+        - "iam.feature.read"
+        - "iam.restrictions.read"
+        - "org.read"
+        - "org.member.read"
+        - "org.member.write"
+        - "org.idp.read"
+        - "org.feature.read"
+        - "user.read"
+        - "user.write"
+        - "user.grant.read"
+        - "user.grant.write"
+        - "user.membership.read"
+        - "user.credential.write"
+        - "user.passkey.write"
+        - "user.feature.read"
+        - "policy.read"
+        - "project.read"
+        - "project.member.read"
+        - "project.member.write"
+        - "project.role.read"
+        - "project.app.read"
+        - "project.member.read"
+        - "project.member.write"
+        - "project.grant.read"
+        - "project.grant.member.read"
+        - "project.grant.member.write"
+        - "session.read"
+        - "session.link"
+        - "session.delete"
+        - "userschema.read"
     - Role: "ORG_USER_MANAGER"
       Permissions:
         - "org.read"