move gotd fork into repo. (#111)

- update to latest telegram layer
- remove some references to fields in tg.Entities that don't exist in
the schema
- originally added here:
https://github.com/beeper/td/commit/820929062a2ba0104397bc01235ab58a9cff780e
  - referenced here
-
https://github.com/mautrix/telegramgo/commit/124f0967ed195b5a380c9bd02e170ada9710dde3
-
https://github.com/mautrix/telegramgo/commit/4205047aab2e0639217148b5d125bfaab668bd8e

pkg/gotd/telegram/cfg_test.go

@@ -0,0 +1,27 @@
+package telegram
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/bin"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/tg"
+)
+
+func TestClient_fetchConfig(t *testing.T) {
+	a := require.New(t)
+	cfg := &tg.Config{
+		ThisDC: 10,
+	}
+	client := newTestClient(func(id int64, body bin.Encoder) (bin.Encoder, error) {
+		a.IsType(&tg.HelpGetConfigRequest{}, body)
+		return cfg, nil
+	})
+
+	a.NoError(client.processUpdates(&tg.Updates{
+		Updates: []tg.UpdateClass{&tg.UpdateConfig{}},
+	}))
+
+	a.Equal(*cfg, client.Config())
+}