docs(developers): add documentation for MessagePack

[JustGodWork]

This pull request introduces comprehensive documentation for the MessagePack integration in FiveM, detailing its features, reserved types, and usage in Lua and JavaScript runtimes. The C# section is marked as TODO to allow future contributions.

This documentation complements citizenfx/fivem#2931, which globally exposes the MessagePack codec (msgpack_pack and msgpack_unpack) to enhance cross-runtime data serialization and deserialization.

Key Updates:

• MessagePack Overview:

  • Introduction to the binary serialization format and its support across Lua, JavaScript, and C#.
  • Features like compact serialization and cross-language compatibility.

• Reserved Extension Types: A table of FiveM-specific types, such as Vector2, Vector3, and others.

• Lua API:

  • Documentation for built-in functions (msgpack.pack, msgpack.pack_args, msgpack.unpack) with practical examples.
  • Guide to adding custom types for serialization.

• JavaScript API:

  • Explanation of global codec functions (msgpack_pack, msgpack_unpack) and custom codec usage.
  • Examples of encoding, decoding, and extending types.

• Example Scenarios: Real-world cases of cross-runtime data handling (Lua to JavaScript, JavaScript to C#, and C# to Lua).

Reason for the Update:

This documentation supports the recent enhancement from citizenfx/fivem#2931, ensuring developers can effectively utilize the MessagePack codec for optimized data handling across all FiveM-supported runtimes. Preview:

The document is located at content/docs/scripting-reference/msgpack.md.

Feedback Requested:

• Suggestions for improving clarity or adding examples.
• Contributions to the C# API section.