feat(enforcer): enable context-aware policy decisions via custom functions

[AKonnyaku]

Policy decisions rely solely on the incoming admission review request body at present. However a more dynamic approach is preferred:

• we should implement custom casbin functions to query the live kubernetes cluster state;
• it will allows policies to verify global constraints such as total pod counts;
• furthermore integrating a kubernetes client within the enforcer helps fetch related resources dynamically;
• caching frequent queries is also recommended to minimize api server load and latency;
• consequently these improvements empower complex policies that require a broader cluster context.