Add a tool to generate OTA from images

During build, we will need to generate an OTA for boot partition using a
16K boot image. Typically, OTA is generated from target_files.zip . To
avoid relying on target_files.zip as a dependency for 16K OTA, add a
tool to generate OTA directly from a raw image.

Test: th, ota_from_raw_img --partition_name boot --output ota.zip $OUT/boot_16k.img
Bug: 293313353
Change-Id: I2076332faf2a8dc573450597efd481e285a49545