[Core V3] Make the bot data path configurable (#879)

* Initial commit

* Fix sentry

* Make cog manager install path work relative to the bot's dir

* Fix downloader to save data relative to the defined data folder

* Fix sentry test

* Fix downloader tests

* Change logfile location

* Add another line to codeowners

* Basic tests

* Fix versioning

* Add in FutureWarning for config file changes

* Add reference to issue

core/cog_manager.py

@@ -270,6 +270,8 @@ class CogManagerUI:
         No installed cogs will be transferred in the process.
         """
         if path:
+            if not path.is_absolute():
+                path = (ctx.bot.main_dir / path).resolve()
             try:
                 await ctx.bot.cog_mgr.set_install_path(path)
             except ValueError: