Agent Activity Information - Frontend

What does this MR do and why?

This MR adds the view for the Agent activity events list (design issue: #277323 (closed)).

The view is available from the Agent page - added as a first tab. Currently, it supports 4 event types:

1. Token created (backend - !74577 (merged))
2. Token revoked (backend not ready yet)
3. Agent connected (backend - !75487 (merged))
4. Agent not connected (backend not ready yet)

The view also has initial support for any unknown event types - it shows the event.kind as a title and the Event occurred <time-ago> as a description.

The view shows an empty state if no activity was stored and a warning alert if the error occurred while fetching the events.

Screenshots or screen recordings

Empty state:

(the fix for the distorted image is here - gitlab-svgs!748 (merged))

Error:

How to set up and validate locally

1. Go to Infrastructure -> Kubernetes clusters
2. Create an agent using the Actions button
3. Click on the agent name to navigate to the Agent details view
4. Verify the Token created event

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.

Related to #340363