Interceptor on server side. See GRPC.Endpoint.
GRPC.Endpoint
@callback call( req :: struct() | nil, stream :: GRPC.Server.Stream.t(), next :: (req :: struct() | nil, GRPC.Server.Stream.t() -> GRPC.Server.rpc_return()), options :: any() ) :: GRPC.Server.rpc_return()
@callback init(options :: any()) :: options :: any()