adding "--fp8_base" to train_network.py

[rippinao]

is this how it should look

def setup_parser() -> argparse.ArgumentParser:
parser = argparse.ArgumentParser()
# ... (existing arguments)

parser.add_argument("--fp8_base", action="store_true", help="Use fp8 as the base precision for mixed precision training.")

# ... (remaining arguments)
return parser