Allow specifying the file name for media uploads

The parameter is optional so this change is backwards compatible

mastodon/Mastodon.py

@@ -2462,7 +2462,7 @@ class Mastodon:
     # Writing data: Media
     ###
     @api_version("1.0.0", "2.9.1", __DICT_VERSION_MEDIA)
-    def media_post(self, media_file, mime_type=None, description=None, focus=None):
+    def media_post(self, media_file, mime_type=None, description=None, focus=None, file_name=None):
         """
         Post an image, video or audio file. `media_file` can either be image data or
         a file name. If image data is passed directly, the mime
@@ -2489,6 +2489,7 @@ class Mastodon:
                                                ' or data passed directly '
                                                'without mime type.')
 
+        if file_name is None:
             random_suffix = ''.join(random.choice(string.ascii_uppercase + string.digits) for _ in range(10))
             file_name = "mastodonpyupload_" + str(time.time()) + "_" + str(random_suffix) + mimetypes.guess_extension(
                 mime_type)