[Feature Request] Promote an existing version to root (replace the base file)

Description An operation that makes an existing version the root of a document: the version's file, checksum, page count and derived artefacts are written onto the root row, the version rows are removed. POST /api/documents/<id>/versions/<version_id>/promote/ with a matching entry in the version list in the UI ("Make this the current version"). Document ID, tags, custom fields, notes and all links stay untouched — that is the property which makes this worth having as a first-class operation rather than delete-and-reupload. Background: since 3.0 a correction creates a version and the original root file stays. There is no way to make a corrected version the root, and the root cannot be deleted either — deleting it trashes its versions with it. For substantive revisions that is right. For cosmetic corrections (a page scanned upside down, pages in the wrong order, a blank back side) it leaves a permanent second copy of the same pages and …