Begin work on a data request API (#4045)

[Core] Data Deletion And Disclosure APIs

 - Adds a Data Deletion API
   - Deletion comes in a few forms based on who is requesting
   - Deletion must be handled by 3rd party
 - Adds a Data Collection Disclosure Command
   - Provides a dynamically generated statement from 3rd party
   extensions
 - Modifies the always available commands to be cog compatible
   - Also prevents them from being unloaded accidentally

redbot/cogs/downloader/downloader.py

@@ -91,6 +91,10 @@ class Downloader(commands.Cog):
         if self._init_task is not None:
             self._init_task.cancel()
 
+    async def red_delete_data_for_user(self, **kwargs):
+        """ Nothing to delete """
+        return
+
     def create_init_task(self):
         def _done_callback(task: asyncio.Task) -> None:
             exc = task.exception()