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.go

@@ -0,0 +1,43 @@
+package telegram
+
+import (
+	"context"
+
+	"go.uber.org/zap"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/constant"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/tg"
+)
+
+// Available MTProto default server addresses.
+//
+// See https://my.telegram.org/apps.
+const (
+	AddrProduction = "149.154.167.50:443"
+	AddrTest       = "149.154.167.40:443"
+)
+
+// Test-only credentials. Can be used with AddrTest and TestAuth to
+// test authentication.
+//
+// Reference:
+//   - https://github.com/telegramdesktop/tdesktop/blob/5f665b8ecb48802cd13cfb48ec834b946459274a/docs/api_credentials.md
+const (
+	TestAppID   = constant.TestAppID
+	TestAppHash = constant.TestAppHash
+)
+
+// Config returns current config.
+func (c *Client) Config() tg.Config {
+	return c.cfg.Load()
+}
+
+func (c *Client) fetchConfig(ctx context.Context) {
+	cfg, err := c.tg.HelpGetConfig(ctx)
+	if err != nil {
+		c.log.Warn("Got error on config update", zap.Error(err))
+		return
+	}
+
+	c.cfg.Store(*cfg)
+}