Add way to download data for the hand demo

[ldcWV]

Motivation and Context

Very small PR that adds a way to download the data needed for the WebXR Hand Demo, which is here: #1366

The command used to download the data will be

python -m habitat_sim.utils.datasets_download --uids webxr_hand_demo --data-path examples/web_apps/webxr_hand_demo/data

This will create examples/web_apps/webxr_hand_demo/data/webxr_hand_demo_dataset with the necessary files inside.

How Has This Been Tested

I ran the dataset downloader and it worked.

Types of changes

• Docs change / refactoring / dependency upgrade
• 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 change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have completed my CLA (see CONTRIBUTING)
• I have added tests to cover my changes.
• All new and existing tests passed.

[eundersander]

LGTM