Draft: [ci skip] Create a resizable panels proof of concept

What does this MR do and why?

Create a resizable panels proof of concept

We are moving the main content to a "panel" and adding another panel to its right which represent an hypothetical Duo Chat panel. The right panel is resizable and therefore affects the main panel's width.

We are also taking this opportunity to demonstrate how we could use container queries to keep the panels' contents responsive relative to the container rather than the viewport.

References

Screenshots or screen recordings

panels_demo

contextual_panel

How to set up and validate locally

1. Run yarn to install the required dependencies.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.