Add script for mixing shared system images with a super image

Bug: 289369510
Test: ./development/gsi/repack_super_image/mix_ssi_with_device_image.py \
      --device-image-files aosp_cf_arm64_phone-img.zip \
      --ssi-files ssi-target_files.zip \
      --misc-info misc_info.txt \
      --ota-tools otatools.zip \
      --output-dir output_dir
Change-Id: I0c16f2e13036a5d66e96309c268214231d56d90b
2 files changed