📖 Improve collapsible code sections and formatting of tutorials

[camilamacedo86]

The following changes impact mainly the tutorials.
To review see:

• https://deploy-preview-5175--kubebuilder.netlify.app/cronjob-tutorial/cronjob-tutorial
• https://deploy-preview-5175--kubebuilder.netlify.app/multiversion-tutorial/tutorial

Documentation Improvements Summary

Changes

New Features:

• Added copy-to-clipboard buttons on code blocks
• Added "(click to expand/collapse)" hints
• Soft collapse styling (no icons, italic text)

Layout:

• Content width: 95% (wider)
• Code padding: 0.5em (reduced)
• Tab-size: 2 (compact)

Content Cleanup:

• Hidden Apache License blocks (23 instances)
• Hidden closing braces in tests
• Removed 3 duplicate collapse markers
• Fixed extra } appearing outside code blocks

Label Updates:

• "Clock" → "Clock Code Implementation"
• "Go imports" → "Imports"
• "Validate object name" → "validateCronJobName() Code Implementation"
• "old stuff" → "Remaining code from "
• "The rest of Spec" → "CronJobSpec Full Code"

Closes: #4862

[k8s-ci-robot]

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