feat: Drop loguru and use builtin logging (#1133)

* Configure simple builtin logging

Changed the 2 existing `print` in the `private_gpt` code base into actual python logging, stop using loguru (dependency will be dropped in a later commit).
Try to use the `key=value` logging convention in logs (to indicate what dynamic values represents, and what is dynamic vs not).
Using `%s` log style, so that the string formatting is pushed inside the logger, giving the ability to the logger to determine if the string need to be formatted or not (i.e. strings from debug logs might not be formatted if the log level is not debug)
The (basic) builtin log configuration have been placed in `private_gpt/__init__.py` in order to initialize the logging system even before we start to launch any python code in `private_gpt` package (ensuring we get any initialization log formatted as we want to)
Disabled `uvicorn` custom logging format, resulting in having uvicorn logs being outputted in our formatted.

Some more concise format could be used if we want to, especially:
```
COMPACT_LOG_FORMAT = '%(asctime)s.%(msecs)03d [%(levelname)s] %(name)s - %(message)s'
```

Python documentation and cookbook on logging for reference:
* https://docs.python.org/3/library/logging.html
* https://docs.python.org/3/howto/logging.html

* Removing loguru from the dependencies

Result of `poetry remove loguru`

* PR feedback: using `logger` variable name instead of `log`

---------

Co-authored-by: Louis Melchior <louis@jaris.io>

private_gpt/__main__.py

@@ -5,4 +5,7 @@ import uvicorn
 from private_gpt.main import app
 from private_gpt.settings.settings import settings
 
-uvicorn.run(app, host="0.0.0.0", port=settings.server.port)
+# Set log_config=None to do not use the uvicorn logging configuration, and
+# use ours instead. For reference, see below:
+# https://github.com/tiangolo/fastapi/discussions/7457#discussioncomment-5141108
+uvicorn.run(app, host="0.0.0.0", port=settings.server.port, log_config=None)