Support Azure custom storage domains
Users of Azure Blob storage, particularly those using Azure China, Azure
Germany, or Azure Government, may need to customize the Azure
endpoint. To support this, we add a custom Azure URL opener that
supports the domain
query parameter. This work has been submitted
upstream: https://github.com/google/go-cloud/pull/2851/files
Documentation for using Azure Blob storage: gitlab!40693 (merged).