Add status and expires columns to secret index page

What does this MR do and why?

Implements #470459 (closed).

This adds the Status and Expiring soon column to the index page for Secrets Management. Last accessed column is also renamed to Last used, and the date format has been updated to reflect the design.

Note that there is no backend integration available, so this MR relies on mock data.

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.

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Before	After

How to set up and validate locally

1. Enable the feature flag for Secrets Management.

   Feature.enable(:ci_tanukey_ui)

2. Visit the Secrets page for your project e.g. <path-to-project>/-/secrets
3. Verify that the status column exists for the table.