Cleanup storage clients

[rylev]

Worked on with @yoshuawuyts ♥

This makes a bunch of the storage clients much simpler and also mirrors more how we do things in Cosmos:

• Combined StorageClient and StorageAccountClient since there wasn't much reason for them to be separate.
• Removed the old authentication code since now all storage clients use the pipeline and thus the Authentication policy
• Removed http_client since we now only use the pipeline
• Removed the external use of Arc since all clients should be cloneable
• Removed a bunch of unnecessary extension traits in favor of just normal methods