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/cdn.go

@@ -0,0 +1,31 @@
+package telegram
+
+import (
+	"crypto/rsa"
+	"encoding/pem"
+
+	"github.com/go-faster/errors"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/crypto"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/tg"
+)
+
+func parseCDNKeys(keys ...tg.CDNPublicKey) ([]*rsa.PublicKey, error) {
+	r := make([]*rsa.PublicKey, 0, len(keys))
+
+	for _, key := range keys {
+		block, _ := pem.Decode([]byte(key.PublicKey))
+		if block == nil {
+			continue
+		}
+
+		key, err := crypto.ParseRSA(block.Bytes)
+		if err != nil {
+			return nil, errors.Wrap(err, "parse RSA from PEM")
+		}
+
+		r = append(r, key)
+	}
+
+	return r, nil
+}