read/load support for isce2/alos2App dense offset

[yunjunz]

Description of proposed changes

• utils.readfile.auto_no_data_value(): support alos2App dense offset

• utils.readfile.get_slice_list(): alos2App use rg/az order, instead of az/rg order in other isce2 applications.

• utils.isce_utils.extract_alosStack_metadata/extract_image_size_alosStack(): support geometry files from alos2App/dense_offset, which have different naming conventions as the ones from InSAR.

• load_data: use absolute path for better robustness

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