Convert network compatibility error to warning

Replace the hard error when running P2P on non-Sepolia networks with a warning message.
This allows users to run P2P on custom networks that are compatible with Starknet v0.12.3 blocks.

node/node.go

@@ -171,7 +171,8 @@ func New(cfg *Config, version string) (*Node, error) { //nolint:gocyclo,funlen
 	var p2pService *p2p.Service
 	if cfg.P2P {
 		if cfg.Network != utils.Sepolia {
-			return nil, fmt.Errorf("P2P can only be used for %v network. Provided network: %v", utils.Sepolia, cfg.Network)
+			log.Warnw("Running P2P on a non-Sepolia network. Network must use blocks compatible with Starknet v0.12.3 (since block 0)",
+				"current_network", cfg.Network)
 		}
 		log.Warnw("P2P features enabled. Please note P2P is in experimental stage")