[feature] Add Dark Mode for developers

Description

This is a feature request for adding a Dark Mode to the WebRTC samples repository. Dark Mode has become a popular and widely adopted UI feature, enhancing user experience, especially in low-light environments. Incorporating Dark Mode into the WebRTC samples would provide a more user-friendly interface and align with modern UI standards.

Steps to reproduce

1. Navigate to any WebRTC sample in the repository.
2. Observe the default light theme applied to the interface.

Expected results

A toggle or automatic detection of the user's system theme to switch between Light and Dark Modes. Add button for dark mode.

Actual results

Currently, all WebRTC samples are presented in a Light Mode without an option for Dark Mode.