Migrate to new azblob sdk for azure blob storage integration

https://github.com/gomods/athens/blob/04e425642e0561795d5a1d6ec7eff8ae91f8e269/go.mod#L13C1-L13C48

The sdk used to integrate with azure blob storage is deprecated and not supported/maintained anymore

https://github.com/Azure/azure-storage-blob-go

Consumers should move to the new SDK instead: 
https://github.com/Azure/azure-sdk-for-go/tree/main/sdk/storage/azblob 
