RFC: Native Azure Blob Storage support with Managed Identity

I'd like to propose native Azure Blob Storage support for Outline, with managed identity as a first-class auth path for Kubernetes workloads. I took a close look through the current storage implementation on main, and this seems like a good fit for the existing BaseStorage abstraction. The main thing I wanted to sanity-check before opening a PR is the upload flow, since that part still appears a bit S3-shaped today. Why There are Azure users who want to use Blob Storage directly without putting an S3-compatibility layer or proxy in front of it. For my use case, the important requirements are: • direct uploads to storage • direct downloads from storage • support for managed identity / workload identity in Kubernetes • no secrets in pods MinIO gateway mode used to be one workaround here, but that is no longer a realistic long-term option. Native Blob support seems like the cleaner path. What I reviewed I read through the current fi…