Use the path .gpteng for storing logs etc per default

[AntonOsika]

Details

Change the workflow of gpt-engineer to be like so:

• Always set memory and archive folders paths to be to the .gpteng folder (which will create it per default if it doesn't exist)
• Always set workspace and input folder paths to be directly in the project path

Checklist

• gpt_engineer/db.py

• Modify the __init__ method of the DB class to set the default paths for the memory and archive folders to be in the .gpteng folder.
• Modify the __init__ method of the DB class to set the default paths for the workspace and input folders to be in the project path.
• Modify the __init__ method of the DB class to create the .gpteng folder if it does not exist.

• tests/test_db.py

• Update any tests related to the default paths of the memory, archive, workspace, and input folders to reflect the changes in the DB class's __init__ method.
• Add a test to verify that the .gpteng folder is created if it does not exist.

• docs/intro/db_class.md

• Document the changes to the default paths of the memory, archive, workspace, and input folders.
• Document the creation of the .gpteng folder if it does not exist.

[ATheorell]

Closing this in favor of #669 and #665