[Proposal] Organize task environment as an example gallery

[yuecideng]

Proposal

Create an organized example gallery for different task environments in the repository. The gallery will showcase existing tasks and can help users understand possible task environments, serving both as reference and inspiration for contributors.

Motivation

• Improve discoverability of example task environments.
• Provide a structured overview for new users and contributors.
• Encourage best practices through curated examples.
• (To be discuss) Move the tasks implementation from embodichain directory. We may refer to Isaac Lab Arena.

Additional context

The example gallery could be a dedicated folder, markdown page, or section in the docs that lists and describes available task environments with links, code snippets, and usage notes.