Use Struct from proto instead of map[string]interface

[NicolasMahe]

The proto are using Struct and map[string]*Value from proto.
The engine should also use it instead of the custom map[string]interface.

• service validation Do not convert proto.Struct to map in order to Validate it #1309
• process Use proto.Struct in the orchestrator #1320
• orchestrator Use proto.Struct in the orchestrator #1320
• ethwallet client Update EthWallet service to latest gRPC API version #1324
• remove convert functions! Update EthWallet service to latest gRPC API version #1324

Then, good stuff that can be done:

• change type of process.filter to Value (currently String)

[NicolasMahe]

I'm closing this issue as the modif has been done in the Engine and we decided to not do it for ethwallet (see related PR for more info).