PictureViewsGenerationWork should not be marked as idempotent

PictureViewsGenerationWork uses an id based on the document id:

        repositoryName + ':' + docId + ':' + xpath + ":pictureView"

And don't override Work#isIdempotent which means that it is defined as an idempotent Work by default.

As a result, when using the StreamWorkManager that handles idempotency, the generated picture is not updated when the blob is updated.

Either the work must override Work#isIdempotent to be marked as non-idempotent.
Either the id must be replaced by a digest of the blob and stays idempotent.