Feature to read RT Dose files

[amithjkamath]

This change includes a new image type called DoseImage which then includes the scaling factor and also reduces the dimensions of dose volumes to be 3D (in case it is 4D by default).

• [ x] New feature (non-breaking change which adds functionality)

Testing Description

The existing tests have been run and nothing breaks (except for an unrelated issue: see
unit/fileio/writing/test_dicom_series_subject_writer.py:64 (test__write_to_zip_4)
img_series_dcm = '/private/var/folders/yr/q_0gpqgs1lq_rtbttpk3n9bh0000gn/T/pytest-of-amithkamath/pytest-0/data10'
empty_folder = '/private/var/folders/yr/q_0gpqgs1lq_rtbttpk3n9bh0000gn/T/pytest-of-amithkamath/pytest-0/data11'

def test__write_to_zip_4(img_series_dcm, empty_folder):
    ds, dicom_path = helper_get_ds(img_series_dcm)
    info = DicomSeriesImageInfo((dicom_path,))
    subject_writer = DicomSeriesSubjectWriter()
    subject_writer._write_to_zip((info,), (("dataset", ds),), empty_folder, "folder_name")

    with ZipFile(os.path.join(empty_folder, "folder_name.zip"), "r") as zip_ref:
        zip_ref.extractall(empty_folder)

    with open(dicom_path, "rb") as file:
        ds_original = pydicom.dcmread(file)

  with open(os.path.join(empty_folder, "img_serie_14.dcm"), "rb") as f:

E FileNotFoundError: [Errno 2] No such file or directory: '/private/var/folders/yr/q_0gpqgs1lq_rtbttpk3n9bh0000gn/T/pytest-of-amithkamath/pytest-0/data11/img_serie_14.dcm'

unit/fileio/writing/test_dicom_series_subject_writer.py:77: FileNotFoundError

• [ x] I have performed a self-review of my code and have run it by Mike already.

[amithjkamath]

This change also fixes the issue: #2

[melandur]

Your extensions is well appreciated