SignedSSVMessage

[MatheusFranco99]

Overview

Introduce SignedSSVMessage, which encapsulates SSVMessage along with a signature and a sender identifier fields.

Changes

• New SignedSSVMesage structure in types
• Flat encoding for SignedSSVMesage
• DecodePubsubMsg now returns a SignedSSVMesage
• MsgValidation adapted to receive a SignedSSVMesage instead of a SSVMessage

Note: though SSVMessage is no longer the transmitted message in the network, the Runner still processes the type SSVMessage in the ProcessMessage function.

Tests

• [x] Encoding
• [x] Valid SignedSSVMessage
• [x] Invalid SignedSSVMessage with no data
• [x] Invalid SignedSSVMessage with empty signature
• [x] Invalid SignedSSVMessage with zero signer
• [x] Invalid SignedSSVMessage with wrong data

Note: this is a non-fork version of #345

[MatheusFranco99]

@y0sher I changed the encoding to match with the implementation one