[twitter] include '4096x4096' as a default image fallback

(closes #2107, closes #1881)

docs/configuration.rst

@@ -2022,7 +2022,7 @@ extractor.twitter.size
 Type
     ``list`` of ``strings``
 Default
-    ``["orig", "large", "medium", "small"]``
+    ``["orig", "4096x4096", "large", "medium", "small"]``
 Description
     The image version to download.
     Any entries after the first one will be used for potential

gallery_dl/extractor/twitter.py

@@ -47,7 +47,7 @@ class TwitterExtractor(Extractor):
         size = self.config("size")
         if size is None:
             self._size_image = "orig"
-            self._size_fallback = ("large", "medium", "small")
+            self._size_fallback = ("4096x4096", "large", "medium", "small")
         else:
             if isinstance(size, str):
                 size = size.split(",")