Handshake is the HandshakeConfig used to configure clients and servers.

VersionedPlugins includes both protocol 5 and 6 because this is the function called in providerFactory (command/meta_providers.go) to set up the initial plugin client config.

GRPCProvider handles the client, or core side of the plugin rpc connection.

GRPCProviderPlugin implements plugin.GRPCPlugin for the go-plugin package.