[Feature Request] Support for CAdES (.p7m) container files extraction during ingestion

Description I would like to propose native support for .p7m files (CAdES - ETSI EN 319 122). These are cryptographic envelopes widely used in Europe (especially in Italy for Public Administration, legal documents, and E-Invoicing) to store digitally signed documents. Currently, if a user drags and drops a .p7m file into the web UI, or places it in the consume folder, Paperless-ngx cannot "see" the content inside. Since the actual document (usually a PDF or XML) is wrapped in a binary layer, OCR and indexing are impossible, making these documents "invisible" to the system search. Other The proposed workflow: 1. Detection: During ingestion (Web UI drag-and-drop, consume folder, or Email), recognize the file via extension or MIME type (application/pkcs7-mime). 2. Transparent Extraction: Use the existing openssl binary (already present in the official Docker image) to extract the payload. 3. Primary Document: The extracted file becomes the main document for …