[Storage] Improve documentation / samples around using non-standard account URLs

[jalauzon-msft]

We get many questions/issues from customers attempting to use non-standard account URLs (CDN, partitioned DNS, custom domains, etc.) so it would seem our documentation about how to handle this scenario could use some improvement. Updating the documentation for client constructors around non-standard account URLs and the when/how to use the credential dictionary would go a long way.

Additionally adding a sample for how to use the dictionary credential for this case would be helpful to direct people towards as well. Something that shows this use case:

credential = {"account_name": "account-name", "account_key": "<account-key>"}
client = BlobServiceClient(
    account_url="https://account-name.zXX.blob.storage.azure.net/",
    credential=credential
)

An extension of this could be to consider updating our automatic account name parsing logic to handle more cases, like partitioned DNS.