provide an initial implementation of the utility

Modify the existing cardsync utility to become a new "instsync" utility.

Part of https://gitlab.developers.cam.ac.uk/uis/devops/iam/ibis/ibis/-/issues/68

This is probably hard to grok as a diff, you might have a better time looking at the resulting file tree.

The CI has been configured to run a sync job on protected branches if PERFORM_SYNC is set. An example of such a sync job can be found at https://gitlab.developers.cam.ac.uk/uis/devops/iam/ibis/institution-mapping-tool/-/jobs/460192.

The sync job uploads to the bucket created in https://gitlab.developers.cam.ac.uk/uis/devops/iam/deploy-identity/-/merge_requests/69.