CORE-5597 Added Metadata Template AVU migrations.

Added an irods-avu-migrator tool that copies old Metadata Template AVUs from the ICAT into the new metadata database, then removes those ICAT AVUs from their target file/folder.
This tool will also remove the obsolete ipc_user_unit_tag unit from all AVUs.
CORE-5597 Updated irods-avu-migrator unit imports.

The irods-avu-migrator will no longer import "ipc-reserved-unit" units into the metadata database.