feat(ske): support stateless WIF kubeconfig login (#1477)

* feat(ske): support stateless WIF kubeconfig login

* fix(ske): address stateless login review feedback

* Update internal/cmd/ske/kubeconfig/login/login.go

Co-authored-by: Marcel Jacek <72880145+marceljk@users.noreply.github.com>

* fix(ske): prefer explicit login configuration

* fix(ske): use shared OIDC token adapters

* fix(ske): refine cluster config precedence

---------

Co-authored-by: Marcel Jacek <72880145+marceljk@users.noreply.github.com>

Author: Galin-Karabadzhakov

docs/stackit_ske_kubeconfig_login.md

@@ -8,6 +8,15 @@ Login plugin for kubernetes clients, that creates short-lived credentials to aut
 First you need to obtain a kubeconfig for use with the login command (first or second example).
 Secondly you use the kubeconfig with your chosen Kubernetes client (third example), the client will automatically retrieve the credentials via the STACKIT CLI.
 
+Project ID and region are resolved with the following precedence:
+
+| Explicit flag | Global config | Exec cluster config | Result |
+| --- | --- | --- | --- |
+| Not set | Set | Not set | Global config |
+| Set | Set | Not set | Explicit flag |
+| Not set | Set | Set | Exec cluster config |
+| Set | Set | Set | Explicit flag |
+
 ```
 stackit ske kubeconfig login [flags]
 ```
@@ -24,13 +33,18 @@ stackit ske kubeconfig login [flags]
   Use the previously saved kubeconfig to authenticate to the SKE cluster, in this case with kubectl.
   $ kubectl cluster-info
   $ kubectl get pods
+
+  Configure an IdP exec provider for a Kubernetes client that does not provide cluster information. In an SKE workload, the CLI automatically uses the projected workload identity token.
+  $ stackit ske kubeconfig login --idp --cluster-name my-cluster --organization-id my-organization-id --project-id my-project-id --region eu01
 ```
 
 ### Options
 
 ```
-  -h, --help   Help for "stackit ske kubeconfig login"
-      --idp    Use the STACKIT IdP for authentication to the cluster.
+      --cluster-name string      SKE cluster name. Used when the Kubernetes exec request does not provide cluster information.
+  -h, --help                     Help for "stackit ske kubeconfig login"
+      --idp                      Use the STACKIT IdP for authentication to the cluster.
+      --organization-id string   Organization ID. Used in IdP mode when the Kubernetes exec request does not provide cluster information.
 ```
 
 ### Options inherited from parent commands