Implement onboarding module for testnet validator enrollment (#3)

* Add proto files for onboarding module

* Add generated proto bindings

* Define onboarding object

* Define the participants state in keeper

* Update genesis file to initialize and export module state to/from genesis

* Add msg to onboard participant

* Register command to enroll participant

* Add functionality to decode ethereum address from signature

* Add comments for messages and fields

* Fix lint errors in proto files

* Add message validation and events in msg_server

* Reuse crypto utils from go-nitro

* Sign entire eth_payload object

* Use google API for rpc method

* Regenerate proto bindings

---------

Co-authored-by: Prathamesh Musale <prathamesh.musale0@gmail.com>

utils/signature.go

@@ -0,0 +1,18 @@
+package utils
+
+import (
+	"github.com/ethereum/go-ethereum/common"
+
+	"github.com/statechannels/go-nitro/crypto"
+)
+
+func DecodeEthereumAddress(message []byte, sig string) (string, error) {
+	if len(sig) > 2 && sig[:2] == "0x" {
+		sig = sig[2:]
+	}
+
+	signature := crypto.SplitSignature(common.Hex2Bytes(sig))
+	ethereumAddress, err := crypto.RecoverEthereumMessageSigner(message, signature)
+
+	return ethereumAddress.String(), err
+}