📖 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

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[vitorfloriano]

The copy button seems to not be working correctly when we insert the code using the directive {{#literatego}}.

As a suggestion, what would happen if we wrapped the directives in a codeblock, like this:

```go
{{#literatego ./getting-started/testdata/project/api/v1alpha1/memcached_types.go}}
```

[vitorfloriano]

Hi @camilamacedo86 I was taking a look at the preview and noticed that the copy button is duplicated in some blocks, like in here:

But in other codeblocks, it isn't, like in here:

It led me to think that mdBook adds the copy button by default. If you take a look at the current state of the docs, that same codeblock that has duplicated buttons already features the button, as seen in here:

The codeblock that does not have a duplicated button does not feature the button in the current docs, as seen in here:

So, IMO, we could investigate what's causing the button to not be rendered in some codeblocks, instead of adding a custom script for that.

[vitorfloriano]

If it's set by default, should we still add this? Also, I can't see the option code-block-copy-button in the mdBook docs, which only mention copyable.

[vitorfloriano]

@camilamacedo86 I suggested ealier that we tried wrapping the {{#literatego}} directives in a codeblock, but that could create another problem: In some parts of the docs, we insert the whole file into a markdown file, and add the rest of the page in the tutorial as comments in that file. If we wrap everything in a codeblock, the docs inserted as comments in those files may not work properly.

And that raises the question: why do we start some parts in a markdown file, then continue the page by inserting comments in the file that was inserted?

As an example, let's consider this page: https://book.kubebuilder.io/cronjob-tutorial/empty-main

We start it here: https://github.com/kubernetes-sigs/kubebuilder/blob/master/docs/book/src/cronjob-tutorial/empty-main.md

Then we insert this file: https://github.com/kubernetes-sigs/kubebuilder/blob/master/docs/book/src/cronjob-tutorial/testdata/emptymain.go

And then we add comments to that file to continue the instructions in the page.

So, couldn't we keep all the instruction in markdown files, and add only the sections of code that we need? That way, we could wrap each section in a codeblock, to be rendered properly, with the copy button.

See: https://rust-lang.github.io/mdBook/format/mdbook.html?highlight=hide#including-portions-of-a-file