Show shared agents in deployment projects

What does this MR do and why?

This MR adds shared agents to the operate -> Kubernetes clusters page. We have two ways of sharing agents - by ci_access and user_access. We want our users to know which agents are available for them in the project.

We want to show all agents in the same list sorted by the creation date. For the shared agents we are adding a 'shared' badge near the name. We don't let users delete shared agents.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Enable kas_user_access feature flag

   Feature.enable(:kas_user_access)

2. Enable expose_authorized_cluster_agents feature flag

   Feature.enable(:expose_authorized_cluster_agents)

3. Enable KAS on your GDK (steps 1-2 from the guide).
4. 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.
5. Add the following configuration inside your project in .gitlab/agents/<your-agent-name>/config.yaml for the user_access agent:

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

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

   gitops:
     manifest_projects:
     - id: <your-group>/<your-project>
   ci_access:
     projects:
     - id: <your-group>/<your-project-to-share-agent-with>

7. 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 (Optional) Deploy the GitLab Agent (agentk) with k3d section to create a local cluster and connect your agent with the cluster.
8. View Operate -> Kubernetes clusters page of the project you are sharing the agent with and verify the change.

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.

Review progress:

• UX review
• frontend developer review
• frontend maintainer review

Related to #395498 (closed)