Merge the Transkribus and file imports

Requires tasks!360 (merged), closes #1303 (closed)

• The transkribus feature flag must be removed entirely from the Ansible playbook before deploying, since the config parser will raise an error for an unknown feature flag.

• DataFiles are limited to 2GiB. We could increase that limit to 5GiB, just like with artifacts. This might still cause trouble for exports of large collections, as it is easy for a Transkribus collection to reach gigabytes.