Make Dockerfile.src representative of GiGL's dir structure

Currently our `Dockerfile.src` does the following `COPY python/gigl gigl`; which leads to weird behaviours where locally during dev and in GiGL CI we have a folder "python" that exists, but in our docker images that folder does not.

To counteract this, we have places where we do unideal path mangling as follows and thus we need to have our `Dockerfile.src` representative of the dir structure in our repo.
```python
python_or_gigl_dir: Final[Path] = Path(__file__).resolve().parent.parent.parent
GIGL_ROOT_DIR: Final[Path] = (
python_or_gigl_dir
if (python_or_gigl_dir / "setup.py").exists()
else python_or_gigl_dir.parent
)
````