Support Azure Blob Storage

[jonyoder]

Our S3 storage support is useful for a wide variety of providers, but not for Azure Blog storage. We should work on adding support for Azure to the rsstorage library.

See https://github.com/rstudio/package-manager/issues/4465.

A number of cloud providers include S3-compatible APIs:

• Google Cloud Storage
• BackBlaze B2
• Cloudflare's announced R2 service
• Smaller cloud provider options: Digitial Ocean Spaces, Scaleway Object Storage, Linode Object Storage
• Minio