Move get_account_information operation

[rylev]

Despite this change being relatively large in terms of number of lines of code changed, it's actually very simple. It's composed of two related changes (and the rest is just making the compiler happy):

• StorageClient::get_account_information was moved to BlobServiceClient. This operation only has to do with the blob storage account and thus should not be on the more general StorageClient. It makes much more sense for it to be in the blob_storage crate.
• The storage crate was composed of the core module and the account module. The account module only contained the code for the get_account_information operation. Since this has moved to another crate, this module can be deleted which leaves the core module all alone. This PR removes the core module and moves all of its contents to the top level of azure_storage crate.

Users will have to make two changes to their code:

• Instead of using the StorageClient to get blob storage account info, they'll need to use the BlobServiceClient.
• If they were importing anything from azure_storage::core, they'll need to just delete core::.

This is the first step in a series of much bigger changes that @gorzell and I are doing together.

[cataggar]

That sounds fine. It does match the documentation.

Aside, that operation does not work with OAuth. I learned that the hard way over the weekend. Azure/azure-sdk-for-net#30761 (comment)

https://docs.microsoft.com/en-us/rest/api/storageservices/get-account-information#authorization

Note: OAuth-based authorization via an Access Token from AAD/MSI or a User Delegation SAS is not supported with this API.