Update installer istio templates 1.26.3

[ivanzati]

📝 Description

Update istio templates for Geti installer

• Issue number: 873

✨ Type of Change

Select the type of change your PR introduces:

• 🐞 Bug fix – Non-breaking change which fixes an issue
• [x ] 🚀 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

Describe how the changes were tested and how reviewers can test them too:

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

✅ Checklist

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• 🔍 PR title is clear and meaningful
• ✍️ PR description clearly explains the changes and their reason
• 📝 I have linked the PR to the corresponding GitHub Issues, if any
• 💬 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

[Copilot]

Pull Request Overview

This PR updates Istio templates from version 1.24.2.1 to 1.26.3.1 for the Geti installer. This is a straightforward version upgrade that ensures the installer uses the latest Istio version.

Key changes:

• Updates Istio image tag from 1.24.2.1 to 1.26.3.1 across all Istio component templates

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
istio-ztunnel-values.yaml.j2	Updates Istio ztunnel component image tag to 1.26.3.1
istio-istiod-values.yaml.j2	Updates Istio istiod component image tag to 1.26.3.1
istio-cni-values.yaml.j2	Updates Istio CNI component image tag to 1.26.3.1

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