Agent status page: add integration status area - iteration 1

What does this MR do and why?

This MR adds an integration status area to the agent details page. It should show the agent connection status and a toggle for more details. It's the first iteration of the integration status area, more integration details are coming within Agent integration status check page (&5787). For now, the list of the details is:

• agent token valid (currently shown when the agent is connected)
• no agent tokens
• CI/CD workflow with restricted access premium feature (it shows the premium badge when it's not available for the current project)

Screenshots or screen recordings

Collapsed state

Agent is connected

Agent is not connected

Agent was never connected

Agent has no tokens

Premium feature is not currently available for the project

How to set up and validate locally

1. Visit project -> Infrastructure -> Kubernetes integrations page
2. Select Connect a cluster button
3. From the modal create a new agent with the default configuration
4. Select this agent from the list to see the details page
5. To connect the agent, follow the instruction from the modal
6. The agent will be created together with the token. To delete the token, from the agent details page select the Access tokens tab and click the delete button.

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
• backend developer review
• backend maintainer review
• frontend developer review
• frontend maintainer review

Related to #363736 (closed) and #363737 (closed)