Upload attachments of a subscription to Google Drive or Sharepoint

**What problem will this feature request solve?**
Some attachments can be blocked by the email provider due to size.

**Describe the solution you'd like.**
Upload attachments of a subscription that is above X mb of size to Google Drive or Sharepoint can be useful for this.

**How does this feature request impact you?**
Requested by a prospect

The issue does not name files, tests, or entry points. Start by locating subscription attachment delivery and the integrations for Google Drive or SharePoint, then clarify the size threshold, authentication, and expected behavior. Done should include a defined upload flow for oversized attachments and coverage for the relevant cases.

Written by the indexing model from the issue text.