Recent deliveries table - UI polish

What does this MR do and why?

UI polish for recent deliveries table on:

• project-level webhooks
• admin-level system hooks

This MR also includes minor docs updated (viewable here: http://main-ee-71788.178.62.207.141.nip.io/ee/user/project/integrations/webhooks.html#troubleshoot-webhooks)

Screenshots or screen recordings

Before	After

How to set up and validate locally

To generate an entry in the "Recent deliveries" table:

Project level:

1. Navigate to a project's Settings > Webhooks.
2. Create a mock webhook (any URL is fine). The new webhook should appear in the table below the form.
3. Click Edit on the webhook
4. Click Test, and wait for the test to finish
5. Refresh the page.

The failed webhook entry should be visible in the table.

Admin level:

Same as above, but navigate to System Hooks from the admin dashboard.

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 #335128 (closed)