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/uploader/source/source.go

@@ -0,0 +1,21 @@
+package source
+
+import (
+	"context"
+	"io"
+	"net/url"
+)
+
+// RemoteFile is abstraction for remote file.
+type RemoteFile interface {
+	io.ReadCloser
+	// Name returns filename. Should not be empty.
+	Name() string
+	// Size returns size of file. If size is unknown, -1 should be returned.
+	Size() int64
+}
+
+// Source is abstraction for remote upload source.
+type Source interface {
+	Open(ctx context.Context, u *url.URL) (RemoteFile, error)
+}