Fix issues with loading config.json when it doesn't exist (#5416)

* catch and handle FileNotFoundError when using --no-instance when config.json does not already exist

* move load_existing_config to data_manager.py

* use load_existing_config in create_temp_config

* Fix import in redbot-launcher

Co-authored-by: jack1142 <6032823+jack1142@users.noreply.github.com>

redbot/launcher.py

@@ -16,13 +16,13 @@ import pkg_resources
 from redbot import MIN_PYTHON_VERSION
 from redbot.setup import (
     basic_setup,
-    load_existing_config,
     remove_instance,
     remove_instance_interaction,
     create_backup,
 )
 from redbot.core import __version__, version_info as red_version_info, VersionInfo
 from redbot.core.cli import confirm
+from redbot.core.data_manager import load_existing_config
 
 if sys.platform == "linux":
     import distro  # pylint: disable=import-error