Add TLS configuration support to Go feature server #6095

Is your feature request related to a problem? Please describe.

When deploying the Feast Go feature server using the official container image and exposing it via gRPC, there is currently no way to configure TLS directly on the Go server (no flags for cert/key similar to the Python feast serve command). This prevents setups where an AWS ALB (or similar load balancer) can speak HTTPS/TLS directly to the Go feature server; instead, TLS must be terminated elsewhere and the Go server must run with plaintext gRPC behind it.

Describe the solution you'd like
Add native TLS support to the Go feature server, including options (flags or env vars) to enable TLS and provide server certificate, key, and basic TLS settings so load balancers can connect over TLS directly.

Describe alternatives you've considered
N/A

Additional context
N/A