Implement a GraphQL subscription API to track a workspace’s state

Problem statement

• A Workspace’s state changes over time.
• The workspaces list should always display a workspace’s current state real-time

Solution

Implement a GraphQL subscription that allows tracking a Workspace’s state in real-time. There is a frontend issue to enhance the Workspaces UI so it uses the GraphQL subscription to display a workspace’s state change in real time: #408378 (closed)

Here is a branch pointing to a commit prior to removal of the subscription logic and placeholder UI from the remote_dev integration branch: https://gitlab.com/gitlab-org/gitlab/-/tree/caw-remote_dev-snapshot-before-placeholder-ui-removal