Set checksum algorithm for import using bin/omero (see #10338)

This PR allows the user (typically sys-admin) to set the checksum algorithm to be used during the image import phase. The setting can be changed using ``bin/omero config set omero.checksum.default``.

Two major TODOs I can see now are:
1) a documentation of the available strings that can be used as checksum algorithms,
2) (post-demo) implementation of other uses cases (e.g. client setting the checksum algorithm in import settings object and passing that to the server).