Add mocked workspace list

What does this MR do and why?

The initial MVC for the Category:Remote Development UI. This UI is currently stubbed and designed to be hooked to mock data as we evolve the backend component in Remote Development feature behind a feature flag (!105783 - merged).

This MR represents the following work:

• Remote Development Beta - Rails Frontend (&9881 - closed)
• A follow up to Add Remote Development entry point - Stubbed UI (!112397 - merged), to ad the smallest list view possible via a local resolver
• List existing Workspaces in GitLab UI (#385139 - closed)

Screenshots or screen recordings

How to set up and validate locally

1. Enable the remote development flag

   Feature.enable(:remote_development)

2. Visit any group http://127.0.0.1:3000/groups/flightjs
3. Click the Workspaces sidebar entry.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #391543 (closed)