Add Ephemeral Credentials TTL Validator Policy

[yrsuthari]

Add simple TTL validator for Kubernetes Secrets

Overview

This PR introduces a simplified Ephemeral Credentials TTL Validator policy that enforces proper credential lifecycle management by requiring TTL annotations on all Kubernetes Secrets. This helps reduce security risks associated with long-lived credentials.

Changes

• Added simple-policy.yaml - a Kyverno ClusterPolicy that enforces TTL annotations on Secrets
• Updated README.md with documentation and testing instructions
• Created test cases that demonstrate policy compliance enforcement

Implementation Details

• Policy runs in Audit mode to report violations without blocking resource creation
• Validates that all Secrets have the secrets.kubernetes.io/ttl annotation
• Excludes system namespaces (kube-system, kube-public)
• Supports Kubernetes duration format for TTL values (e.g., "24h", "7d")

Testing

Policy has been tested with:

• Compliant Secret with TTL annotation
• Non-compliant Secret without TTL annotation
• Verification via policy events and violation reports

Security Benefits

• Reduces risk of forgotten credentials becoming security blind spots
• Limits attacker access window when credentials are compromised
• Establishes audit trails for credential renewal
• Aligns with zero-trust security principles and industry best practices