feat(kubernetes): simplify navigation access, update labels, and add welcome info box

[ArtieReus]

Summary

This PR modernizes the Kubernetes navigation in Elektra by removing project tag dependencies, restructuring access control for broader availability, updating labels for clarity between legacy and new services, and adding a welcome info box to guide users transitioning to the new Kubernetes (Gardener) UI.

Changes Made

• Removed project tag requirement: Eliminated the persephone project tag dependency for Kubernetes (Gardener) navigation visibility
• Updated access control: Production and canary landscapes are now globally accessible; QA landscape remains restricted to qa-de-1
  region only
• Updated navigation labels:
  • Legacy Kubernikus: "Kubernetes" → "Kubernetes (Legacy)"
  • Primary Gardener: "Kubernetes (Gardener)" → "Kubernetes"
  • Canary: "Kubernetes (Gardener Canary)" → "Kubernetes (Canary)"
  • QA: "Kubernetes (Gardener QA)" → "Kubernetes (QA)"
• Added welcome info box: new: Displays on production landscape only, informing users about the Gardener platform and how to access legacy
• Add a welcome info box: legacy:
  • Suggested wording:
    • Title: A new managed Kubernetes service is available.
    • Text: You are currently using our legacy managed Kubernetes service. We’re pleased to announce a new service powered by Gardener, offering an improved cluster management experience. Your existing clusters remain accessible here on the legacy service. We’ll notify you in advance of any migration steps and sunset timeline. In the meantime, nothing changes for you should you choose to continue using the legacy Kubernetes platform.
• Both info boxes use @domain_config&.plugin_hidden? checks to prevent displaying cross-references to services that aren't available by domain config.

Kubernikus clusters

• Updated page titles: Removed "(Gardener)" suffix from main toolbar titles for cleaner UI

Related Issues

• Issue: (add issue number if applicable)

Screenshots (if applicable)

This is just shown within the new kuberntesplugin and prod landscape and when the legacy plugin is available:

This is just shown within the legacy kubenetes plugin if new already available

Checklist

• I have performed a self-review of my code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have made corresponding changes to the documentation (if applicable).
• My changes generate no new warnings or errors.

[ArtieReus]

Setting to draft and waiting for the approval