[feature] allow importing books with --automerge overwrite

[frrad]

I would like to be able to import a book which is a more recent version but otherwise a duplicate of a book already in my library.

Ideally for my use case I would like to call calibredb add --automerge overwrite

It would be great if there were some knob where I can configure the argument here

Calibre-Web-Automated/scripts/ingest_processor.py

Line 179 in 4951b29

subprocess.run(["calibredb", "add", book_path, "--automerge", "new_record", f"--library-path={self.library_dir}"], check=True)

[frrad]

(just edited to reflect the fact that the 3.0.1 release addressed part of what was in this issue originally)