Re-organize file structure

[rodrigodelazcano]

Description

Re-organize the file tree and naming for Fetch and Shadow Hand environments. The objective of these changes is to follow a standard entrypoint path for registering environments. This facilitates the auto-generation of environment documentation for the website. The entrypoint path follows the sturcture gymnasium_robotics.envs.env_type.env_name:EnvClass, i.e. FetchPickAndPlace-v2 -> gymnasium_robotics.fetch.pick_and_place: MujocoFetchPickAndPlaceEnv

This PR also makes some other minor changes like:

• Auto generate docs for Shadow Hand and Fetch
• Moving citations from README to documentation
• Merging Shadow Hand environment types, non-touch and touch sensor

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Screenshots

Please attach before and after screenshots of the change if applicable.

Checklist:

• I have run the pre-commit checks with pre-commit run --all-files (see CONTRIBUTING.md instructions to set it up)
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes