add global logger at __init__.py with RichHandler

[vkehfdl1]

close #42

I add global logger at autorag/init.py.
But, when you use it, do not import directly from autorag/init.py because it will potentially occur circular import error.
Instead, you can get logger like below code. Remember logger instance have same name is singleton.

import logging
logger = logging.getLogger("AutoRAG")

I use RichHandler instead of StreamHandler for beautiful formatting.
Plus, I use rich exception for beautiful inspection while debugging.
You can see rich logging by deleting last two lines of your pytest.ini
Change pytest.ini looks like this.

[pytest]
env =
    OPENAI_API_KEY=sk-xxxxxxxxxxxxxxxx

log_cli=true
log_cli_level=INFO

[bwook00]

LGTM

[Eastsidegunn]

LGTM.
rich handler docs