Draft: feat(metrics): Added gRPC metrics

What?

This merge request adds new gRPC metrics functionality.

New Metrics System: A complete gRPC metrics package was added that integrates with Prometheus monitoring. This new system can track request/response sizes, request duration, and other performance metrics for gRPC services. It includes a factory pattern for creating metrics collectors and interceptors that automatically measure gRPC calls.

Enhanced Monitoring: The new metrics system provides both unary (single request/response) and streaming gRPC call monitoring, with configurable histogram buckets for different measurement types.

Why?

Part of: gitlab-com/gl-infra/tenant-scale/cells-infrastructure/team#54

How to set up and validate locally

1. Checkout the branch vg/grpc_metrics of topology-service
2. Run topology service locally

./env.sh null go run ./cmd/topology-service serve

3. Fire a couple of gRPC requests using grpcurl

grpcurl --plaintext \
            :9097 \
            grpc.health.v1.Health/Check
{
  "status": "SERVING"
}

4. Check the metrics endpoint

curl http://localhost:9098/metrics