Service private key is not correctly set when public key is present

[devbugging]

Problem

Using flags to set private and public key is causing private key to be ignored and not set on the configuration object.

Steps to Reproduce

Pass both values --service-priv-key and --service-pub-key and check what was the private key that was actually set.

Acceptance Criteria

The private key should be set when passed using a flag.

Context

The code processing configuration private and public key is faulty as seen here: https://github.com/onflow/flow-emulator/blob/master/cmd/emulator/start/start.go#L95-L118

	if len(conf.ServicePublicKey) > 0 {
		checkKeyAlgorithms(serviceKeySigAlgo, serviceKeyHashAlgo)

		servicePublicKey, err = crypto.DecodePublicKeyHex(serviceKeySigAlgo, conf.ServicePublicKey)
		if err != nil {
			Exit(1, err.Error())
		}
	} else if len(conf.ServicePrivateKey) > 0 {
		checkKeyAlgorithms(serviceKeySigAlgo, serviceKeyHashAlgo)

		servicePrivateKey, err = crypto.DecodePrivateKeyHex(serviceKeySigAlgo, conf.ServicePrivateKey)
		if err != nil {
			Exit(1, err.Error())
		}

		servicePublicKey = servicePrivateKey.PublicKey()
	} else {
		servicePrivateKey, serviceKeySigAlgo, serviceKeyHashAlgo = getServiceKey(
			conf.Init,
			serviceKeySigAlgo,
			serviceKeyHashAlgo,
		)
		servicePublicKey = servicePrivateKey.PublicKey()
	}