Cannot use otbtf TFrecords without gdal

When on a system without gdal, the following fails:

from otbtf.tfrecords import TFRecords
# import otbtf.tfrecords.TFRecords  # this also fails

Rasing:

raceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/linkhome/rech/gentet01/ube33sw/otbtf/otbtf/__init__.py", line 24, in <module>
    from otbtf.dataset import Buffer, PatchesReaderBase, PatchesImagesReader, IteratorBase, RandomIterator, Dataset, \
  File "/linkhome/rech/gentet01/ube33sw/otbtf/otbtf/dataset.py", line 30, in <module>
    from otbtf.utils import read_as_np_arr, gdal_open
  File "/linkhome/rech/gentet01/ube33sw/otbtf/otbtf/utils.py", line 23, in <module>
    from osgeo import gdal
ModuleNotFoundError: No module named 'osgeo'

This is because in __init__.py, there is some pieces of code that rely on gdal:

from utils import read_as_np_arr, gdal_open
from otbtf.dataset import ...

To fix this issue, we would need an empty init.py. However, there is a drawback: all functions/classes would be split depending on their file (dataset, utils or tfrecords). Thus, backward comp would break, because stuff like import otbtf.Dataset would move to otbtf.dataset.Dataset