Improve yolov8 config

[GuillaumeBruand]

• Allow user to pass custom yolo config through the standard yolo yaml config file
• Pass the confidence threshold to inner model to avoid prefiltering with default yolo threshold=0.25

For yolov8, the predict configuration is given at inference time.
We can pass full parameters using the "cfg" argument and a yaml configuration file.

Passing the "conf" argument using confidence_threshold also avoids to prefilter boxes in the underlying yolo model.

Fixes #1030.

[fcakyon]

Amazing contribution @GuillaumeBruand ! 🚀

Please fix the errors raised in tests by:

• Install required development packages:

pip install -e ."[dev]"

• Reformat with black and isort:

python -m scripts.run_code_style format

Then commit+push

[fcakyon]

Thanks for the amazing contribution @GuillaumeBruand !