include CHECKSUM_TYPES in kojikamid.py, and use it when validating checksums of downloaded files
    
    The Koji data model has been updated to support multiple checksum types. These are listed in the
    CHECKSUM_TYPES enum in koji/__init__.py, but are not available in kojikamid.py. This change
    copies the Enum class and the CHECKSUM_TYPES enum into kojikamid at build time, and uses it when
    validating the checksums of downloaded files.