ITEP-68660 online installation of k3s + handling local registry

[jcchr]

📝 Description

Replace offline installation of k3s with its online counterparts. It reduces the number of images that have to be downloaded - reducing the time required to install the platform.
Additionally - it allows to define a local registry for external components.

✨ Type of Change

Select the type of change your PR introduces:

• 🐞 Bug fix – Non-breaking change which fixes an issue
• 🚀 New feature – Non-breaking change which adds functionality
• 🔨 Refactor – Non-breaking change which refactors the code base
• 💥 Breaking change – Changes that break existing functionality
• 📚 Documentation update
• 🔒 Security update
• 🧪 Tests

🧪 Testing Scenarios

Check if after the change there are no superfluous images downloaded - like docker.io/rancher/klipper-helm, docker.io/rancher/klipper-lb, docker.io/rancher/mirrored-library-traefik

• ✅ Tested manually
• 🤖 Run automated end-to-end tests

✅ Checklist

Before submitting the PR, ensure the following:

• 🔍 PR title is clear and descriptive
• 📝 For internal contributors: If applicable, include the JIRA ticket number (e.g., ITEP-123456) in the PR title. Do not include full URLs
• 💬 I have commented my code, especially in hard-to-understand areas
• 📄 I have made corresponding changes to the documentation
• ✅ I have added tests that prove my fix is effective or my feature works