Docs: update "Customizing library models for <lang>" to cover JSON data extensions

[nickrolfe]

Update the documentation for all languages to cover the JSON data extension format that will be supported (and preferred for performance reasons) in an upcoming CodeQL CLI release.

[Copilot]

Copilot review overview

🟡 Changes recommended

Two Go examples incorrectly target the nonexistent codeql/go pack instead of codeql/go-all.

Review effort: Balanced
Findings: 1

Open (1)

• Use valid codeql/go-all extension target · New

What changed in this PR

Updates library-modeling guides to document JSON data extensions while retaining YAML syntax references.

Changes:

• Adds JSON format guidance and converts examples to JSON.
• Updates JSON booleans and comment syntax.
• Updates the GitHub Actions model-pack example to load JSON files.

File	Description
customizing-library-models-for-rust.rst	Adds Rust JSON examples.
customizing-library-models-for-ruby.rst	Adds Ruby JSON examples.
customizing-library-models-for-python.rst	Adds Python JSON examples.
customizing-library-models-for-javascript.rst	Adds JavaScript JSON examples.
customizing-library-models-for-java-and-kotlin.rst	Adds Java/Kotlin JSON examples.
customizing-library-models-for-go.rst	Adds Go JSON examples.
customizing-library-models-for-csharp.rst	Adds C# JSON examples.
customizing-library-models-for-cpp.rst	Adds C/C++ JSON examples.
customizing-library-models-for-actions.rst	Adds GitHub Actions JSON examples and configuration.

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