[Feature Request] View and edit expiration of existing document share links

Description Problem Statement Currently, Paperless-ngx allows users to generate public share links for documents with an optional expiration date. However, once a link is created: 1. The expiration date is no longer visible in the UI. 2. There is no way to edit or extend the expiration date of an existing link. Users must delete the link and generate a new one, which changes the URL slug and breaks any external references already shared with third parties. Proposed Solution I propose enhancing the share link management flow within the document detail page (the "Send" action modal): 1. Display Active Link Details: Display the generated share link URL alongside its configured expiration date/time so that users can verify its validity. 2. Edit Expiration: Allow users to update the expiration date of an active share link in-place (updating the backend model without changing the slug/URL). 3. Backend/API Support: Ensure the API endpoint for ShareLink supports P…