fix: restore deprecated interceptor modules (#292)

Since PR #289, the `GRPC.ServerInterceptor` and
`GRPC.ClientInterceptor` is suddenly remove. This could make breaking
changes. This changes restore it and add deprecated to `@moduledoc` to
those interceptors.

lib/grpc/client/interceptor.ex

@@ -1,3 +1,20 @@
+defmodule GRPC.ClientInterceptor do
+  @moduledoc """
+  Interceptor on client side. See `GRPC.Stub.connect/2`.
+  """
+
+  @moduledoc deprecated: "Use `GRPC.Client.Interceptor` instead"
+
+  alias GRPC.Client.Stream
+
+  @type options :: any()
+  @type req :: struct() | nil
+  @type next :: (Stream.t(), req -> GRPC.Stub.rpc_return())
+
+  @callback init(options) :: options
+  @callback call(stream :: Stream.t(), req, next, options) :: GRPC.Stub.rpc_return()
+end
+
 defmodule GRPC.Client.Interceptor do
   @moduledoc """
   Interceptor on client side. See `GRPC.Stub.connect/2`.

lib/grpc/server/interceptor.ex

@@ -1,3 +1,21 @@
+defmodule GRPC.ServerInterceptor do
+  @moduledoc """
+  Interceptor on server side. See `GRPC.Endpoint`.
+  """
+
+  @moduledoc deprecated: "Use `GRPC.Server.Interceptor` instead"
+
+  alias GRPC.Server.Stream
+
+  @type options :: any()
+  @type rpc_return ::
+          {:ok, Stream.t(), struct()} | {:ok, Stream.t()} | {:error, GRPC.RPCError.t()}
+  @type next :: (GRPC.Server.rpc_req(), Stream.t() -> rpc_return())
+
+  @callback init(options) :: options
+  @callback call(GRPC.Server.rpc_req(), stream :: Stream.t(), next, options) :: rpc_return
+end
+
 defmodule GRPC.Server.Interceptor do
   @moduledoc """
   Interceptor on server side. See `GRPC.Endpoint`.