fix: allow edge case of quickstart before run on first install

[cpacker]

Please describe the purpose of this pull request.

If the user runs quickstart before run on a fresh install (with no home dir created yet), you'll get an error on run:

  File "/home/cpacker/anaconda3/lib/python3.9/site-packages/memgpt/utils.py", line 182, in list_agent_config_files
    files = os.listdir(agent_dir)
FileNotFoundError: [Errno 2] No such file or directory: '/home/cpacker/.memgpt/agents'

To fix this, the user has to then:

• run memgpt configure (to trigger MemGPTConfig.create_config_dir())
• run memgpt quickstart (to reset the values to the desired defaults)

Note @sarahwooders: we should probably add safeguards into list_agent_config_files to prevent crashing on empty dirs?

How to test

Delete ~/.memgpt, run memgpt quickstart as your initial command. On main, this bricks. On this PR it's fixed.

Have you tested this PR?

Yes