Add option to skip Checksum verif between doc storage and Redis #751

[fflorent]

Context

See #751, we faced an issue where the checksum stored in Redis does not match the one of the document. This is due to the fact that the S3 upload finished but the server crashed before storing the checksum in redis.

So Redis had the checksum of the previous version of the document.

Solution

As suggested in the issue, it should be wise to just log a warning telling that the checksum does not match.

However there is some uncertainty around this. I propose to offer an experimental flag until we are comfortable with just warning the user (if that may be of some help until then?).

[fflorent]

Closing for now, I have doubts about the usefulness of this PR.

[fflorent]

Thanks @paulfitz, I have taken into account your remarks!