Server-Side Protocol Version Restriction (RESP2/RESP3)

### Feature request type

## Summary
Add ability to restrict which RESP protocol versions (RESP2 or RESP3) clients can use when connecting to Garnet server.

## Motivation

### Business Use Case
In enterprise environments, organizations need to:
- **Enforce standardization** across client applications
- **Control protocol upgrades** in a phased manner
- **Prevent legacy clients** from connecting to RESP3-only infrastructure
- **Ensure compatibility** by blocking RESP3 clients when infrastructure doesn't support it
- **Security compliance** - some policies require specific protocol versions

### Current Limitation
Currently, Garnet accepts both RESP2 and RESP3 connections without restriction. The protocol is negotiated by the client via the `HELLO` command, and the server always accepts the client's preference.

**Problem:** Server administrators have no way to enforce protocol version policies.

### Describe the solution you'd like

## Proposed Solution
### Command-Line Arguments
Add new command-line parameters to restrict protocol versions:
GarnetServer --allowed-protocols RESP3 # RESP3 only GarnetServer --allowed-protocols RESP2 # RESP2 only GarnetServer --allowed-protocols BOTH # Both (default)

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

Start by locating GarnetServer's command-line argument parsing and the HELLO command's RESP version negotiation path. Trace how the default accepts both RESP2 and RESP3, then define enforcement for RESP2-only, RESP3-only, and the default BOTH mode; done means disallowed client protocol selections are rejected while allowed selections continue to work.

Written by the indexing model from the issue text.