Draft: Add support for websocket cluster connection

What does this MR do and why?

This MR adds support for the Watch Aggregator API for watch requests instead of the Kubernetes watch API. This feature is behind a feature flag use_websocket_for_k8s_watch as it's a work in progress. Within the current MR, we add WebSocket support for the pods, services, and events. Other resources will be updated separately. For now, we only check the WebSocket messages with the type event, support for the error and stop messages will be added separately.

MR acceptance checklist

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

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

No visual changes.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Prerequisites:

• NGINX, loopback interface, and HTTPS set up on your GDK
• Docker instance
• KAS enabled on GDK (steps 1-2 from the guide).

1. Visit the Project -> Infrastructure -> Kubernetes clusters page and create an agent following the instructions from the modal.

   • Select the "Connect a cluster" button
   • The modal should pop up
   • In the modal select "Select an agent or enter a name to create new"
   • You probably won't have any configured agents to show up in the list, create a new one by typing the name of your choice
   • The button should appear at the bottom of the list saying "Create agent: <your-agent-name>"
   • Select the button and click "Register" in the next view.
   • Save the token to use it in the next point.

2. Add the following configuration inside your project in .gitlab/agents/<your-agent-name>/config.yaml for the user_access agent:

   user_access:
     access_as: 
       agent: {}
     projects:
     - id: <your-group>/<your-project-to-share-agent-with>

3. Note that the shared agents should be connected to the cluster in order to appear in the list. Please follow points 3-8 from the guide and then the Deploy the GitLab Agent (agentk) with k3d section to create a local cluster and connect your agent with the cluster.

4. Visit Project -> Operate -> Environments

5. Create/Edit an environment using the UI

6. Select an agent from the dropdown in the Environments settings page and save the change.

7. Visit the Environments page and visit the environment details page for the environment that has an associated agent.

8. Enable feature flag use_websocket_for_k8s_watch for your project:

   Feature.enable(:use_websocket_for_k8s_watch, Project.find(<project_id>))

9. Validate the dashboard is working using WebSocket connection. Validate that a single WebSocket is opened for multiple resources. Click on pods to view the events in the pod details drawer.