[Feature Request] Batch/digest option for workflow notifications instead of one per document

Description Affected version: paperless-ngx 2.20.15 Summary ------- Workflows only fire per-document — there's no way to get a single batched notification for "N documents were processed since last check" instead of one notification per document. For anyone running an OCR/AI-tagging pipeline that processes several documents a day, per-document notifications get noisy fast. What we ended up building instead ----------------------------------- Since paperless-ngx has no native way to do this, we built an external script that polls the REST API for documents matching a tag with a modified timestamp newer than the last run, and sends one combined notification (count + title list) via a scheduled job. It works, but it's an external polyfill for something that feels like it should be possible natively — especially since the workflow/webhook system already has all the information needed per-document, just not a way to accumulate it. Feature reques…