Add new binary arrays for orbit directions to the datacubes

[mliukis]

Using granules img_pair_info variable, add binary array for 'ascending/descending' to the corresponding layers of the datacubes.

Call new variables:

ascending1 = [true/false]
ascending2 = [true/false]

[mliukis]

Only S1 granules have orbit direction information available: img_pair_info.flight_direction_img[12]

[alex-s-gardner]

Only S1 granules have orbit direction information available: img_pair_info.flight_direction_img[12]

This is OK, I don't think we need a/d for optical sensors

[mliukis]

@alex-s-gardner should we keep the new data variables names consistent with other granule names such as img_pair_info.flight_direction_img1?
So make it:

ascending_img1 = [true/false]
ascending_img2 = [true/false]

and have values set to missing_value = 255 for other than S1 missions?