Add Kubernetes overview tab on environments details page

What does this MR do and why?

This MR is part of a larger effort to move the cluster UI under the environment details page.

The first MR of this series - Add Deployments history tab on environments det... (!143865 - merged)

The current MR adds the Kubernetes overview tab to the Environment details page. It uses the existing Kubernetes overview (currently available in a collapsible section on the Environments index page). The existing Kubernetes overview component gets some UI changes:

• Removes the Calendar icon
• Combines time with the connection status for the agent.

As part of this MR we also add an empty state according to the design (in the issue).

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

1. Empty state

   

2. Success state

   

3. Error state

   

How to set up and validate locally

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 -> Operate -> Environments

2. Create/Edit an environment using the UI

3. Visit the Project -> Infrastructure -> Kubernetes clusters page and create an agent following the instruction 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.

4. 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>

5. 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.

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 to validate the success view.

8. Visit the Environments page and visit the environment details page for the environment that has no associated agent to validate the empty state.

Related to #431746 (closed)