cert-manager: Add certificate expiry visibility and renewal status alerts (#705)

[harkirath1511]

Closes #705

Adds certificate expiry tracking and renewal status alerts to the cert-manager plugin. Certificates are now shown with color-coded expiry states and a new Overview dashboard surfaces certificates that need attention.

Changes

New: Certificate Expiry Utility (src/utils/certificateExpiry.ts)

• Pure utility functions for computing expiry level, formatting human-readable labels, and filtering certificates that need attention
• Thresholds: > 30 days → ok, ≤ 30 days → warning, < 7 days → critical, past date → expired

New: CertificateExpiryLabel Component

• Tooltip-wrapped StatusLabel that renders color-coded expiry state
• 🟢 Green for healthy, 🟡 Yellow for expiring soon, 🔴 Red for critical/expired

New: Overview Page (/cert-manager/overview)

• Dashboard with 3 summary cards: Total certificates, Expiring soon (≤ 30 days), Expired
• Table of certificates needing attention with direct links to their detail pages
• The cert-manager sidebar entry now lands on this Overview page

Updated: Certificates List

• Expires In column replaces the raw date with the new color-coded CertificateExpiryLabel
• Secret column now links directly to the related Kubernetes Secret
• Sort on Expires In handles missing/invalid dates gracefully (pushed to end)

Updated: Certificate Detail

• Not After field replaced with CertificateExpiryLabel for visual consistency
• Secret Name field now navigates to the Kubernetes Secret

Refactor: SecretNameLink

• Extracted reusable SecretNameLink component in CommonComponents.tsx
• Used across List, Detail, and SecretKeySelectorComponent (DRY)

Tests

Added 9 unit tests for the expiry utility covering all branches:

• Unknown/invalid notAfter
• ok / warning / critical / expired levels
• Boundary conditions (exactly 7 days, exactly 30 days)
• needsExpiryAttention helper
• formatExpiryLabel formatting

Test Files  1 passed (1)
Tests       9 passed (9)

Screenshots

Checklist

• Human-readable expiry column added
• Expiry status colors work correctly
• Overview widget shows expiring certificates
• Secret links navigate correctly
• i18n keys added to locales/en/translation.json
• Unit tests added