Support uploading of dumps / attachments to Azure Blob Storage

### Problem Statement

At the point of crash dump creation, a studio doesn't have the ability to send it to Azure (or anywhere else) at the point Sentry expects to upload it. However, if it exceeds the supported limit (it will fail) or if there is a case the studio has a business need to store it elsewhere there doesn't seem to be any other options available. A feature / workaround would be to opt into a path to send-to optional Azure storage.

### Solution Brainstorm

An integration flow native to the attach scenario that allows a studio to point to an alternate storage location programmatically.

### Product Area

APIs

Start by mapping the crash-dump attachment flow from creation through Sentry's expected upload point, then identify where an optional Azure storage destination could be configured programmatically. Clarify the supported size limits, alternate-storage behavior, and API contract with the issue's stakeholders; done means an agreed integration flow that covers these cases.

Written by the indexing model from the issue text.