🚸 Enable optional full content hashing

[falexwolf]

A user now ran into a case where the filename, timestamp, first 50MB and last 50MB of a file was the same, but something 'in the middle of the file' had changed. This happened for an SQLite file.

We should enable to optionally hash the full content, even if that runs for a while.

[ap--]

For s3 you have etag generated automatically on upload so it would be easy compute etag locally for that if the quickhash collides, and then compare again.