Add support for websocket rpc connections

[itsahedge]

As of version 2.0.2, the Go SDK does not support websocket rpc connections because in the getDefaultRpc() function, it checks:

if strings.HasPrefix(rpcUrlorName, "http") {
	return rpcUrlorName, nil
} else {
	return "", fmt.Errorf("invalid rpc url or chain name: %s", rpcUrlorName)
}

Adding websocket support would make it easier to handle listening on contract events.

example: wss://goerli.infura.io/ws/v3/{your-infura-project-id}

solution:

func getDefaultRpcUrl(rpcUrlorName string) (string, error) {
	switch rpcUrlorName {
	case "mumbai":
		return defaultRpc("mumbai")
	case "goerli":
		return defaultRpc("goerli")
	case "polygon":
		return defaultRpc("polygon")
	case "mainnet", "ethereum":
		return defaultRpc("ethereum")
	case "fantom":
		return defaultRpc("fantom")
	case "avalanche":
		return defaultRpc("avalanche")
	case "optimism":
		return defaultRpc("optimism")
	case "optimism-goerli":
		return defaultRpc("optimism-goerli")
	case "arbitrum":
		return defaultRpc("arbitrum")
	case "arbitrum-goerli":
		return defaultRpc("arbitrum-goerli")
	default:
		if strings.HasPrefix(rpcUrlorName, "http") || strings.HasPrefix(rpcUrlorName, "wss") {
			return rpcUrlorName, nil
		} else {
			return "", fmt.Errorf("invalid rpc url or chain name: %s", rpcUrlorName)
		}
	}
}

[joaquim-verges]

Thank you for reporting this @itsahedge - would you like to put up a PR for this? Contributions are always welcome!

[itsahedge]

|| strings.HasPrefix(rpcUrlorName, "wss")

#132