docs: update document for dataset schema

[ktro2828]

What

This PR updates the document for T4 dataset schema definitions.

These updates are basically moved from tier4_perception_dataset/docs/t4_format_3d_defailed.md.

Notes for Reviewers

You can check the preview of the document on your local device as follows:

mkdocs serve

[Copilot]

Pull Request Overview

This PR updates documentation for the T4 dataset schema by adding comprehensive schema documentation moved from an external repository. The changes create a dedicated dataset schema section in the documentation with detailed table definitions and sensor data specifications.

• Adds new documentation structure for dataset schema with three main sections
• Creates detailed schema table definitions for mandatory and optional tables
• Adds sensor data format specifications for LiDAR, camera, and radar data
• Removes references to external schema documentation

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
mkdocs.yaml	Adds new "Dataset Schema" navigation section with three subsections
docs/schema/table.md	Comprehensive documentation of schema table definitions and data types
docs/schema/index.md	Overview of dataset directory structure and schema organization
docs/schema/data.md	Detailed specifications for LiDAR, camera, and radar sensor data formats
docs/index.md	Removes reference to external dataset format documentation
README.md	Removes reference to external dataset format documentation and updates navigation

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[ktro2828]

I need to add a new field for SampleData after #175 has been merged.

[ktro2828]

info_filename field has been added into the document of SampleData in 5a506d4