Expand getversion RPC call output with network's magic number

[roman-khimov]

Summary or problem description
As all hashes and signatures are network-dependent now all clients need to know the magic number of the network. This magic number can be configured explicitly in the client, but I think we can do a bit better than that by making it discoverable from the server.

Do you have any solution you want to propose?
I don't think it's worth another RPC call, we can just add a magic field to the getversion RPC call return value.

In general, this follows the same line as #355 (and maybe intersects a bit with intentions of neo-project/neo#1977), I'd really like the client to have exactly one thing to configure --- RPC endpoint to use, everything else it needs should be available from that.

Where in the software does this update applies to?

• RPC (HTTP)

[realloc]

This feature is needed for NeoFS to work with sidechain. Sharing or hardcoding common privnet magic number may be a security issue.

[shargon]

Agree