Various Config and Mongo Driver fixes (#2795)

- Fixes defaults being mixed into custom groups above the document level when doing `Group.all()`
- Fixes `Config.clear_all()` with Mongo driver
- Fixes `Group.set()` with Mongo driver on custom groups above the document level
- Fixes `IdentifierData.custom_group_data` being set to the wrong thing in `BaseDriver.import/export_data` (although this was an inconsequential bug)

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

redbot/core/drivers/red_json.py

@@ -1,5 +1,4 @@
 from pathlib import Path
-from typing import Tuple
 import copy
 import weakref
 import logging
@@ -156,7 +155,7 @@ class JSON(BaseDriver):
                     category,
                     pkey,
                     (),
-                    custom_group_data.get(category, {}),
+                    custom_group_data,
                     is_custom=category in custom_group_data,
                 )
                 update_write_data(ident_data, data)