Render environments as labels in Secrets table

What does this MR do and why?

Follow-up from !154536 (merged).

Because we changed the mock data in !154536 (merged), scoped labels (which are the same as environments, making this data redundant) are no longer shown. This MR fixes that so we render environments as scoped labels in the Secrets table.

Note that there's no backend integration for the Secrets Manager yet, so we're just working with mock data for now.

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.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Enable the ci_tanukey_ui feature flag for your project.

   Feature.enable(:ci_tanukey_ui, <project>)

2. Visit <path-to-project>/-/secrets.