Add support to storage_blob_host configuration

[igosneves]

Adding support for configuration storage_blob_host, which makes the gem compatible with azurite. I've adopted this variable name given it is the same supported by azure-storage-blob

I was able to runtime test this in my application's environment, using azure-blob gem. To test this with azurite, the following needs to be done:

• Run azurite locally. A quick way to have it running locally with docker is:
  docker run -p 10000:10000 mcr.microsoft.com/azure-storage/azurite azurite-blob --blobHost 0.0.0.0 --blobPort 10000
  If you need more configuration options you can check azurite's official documentation here
• Using Microsoft Azure Storage Explorer, connect to your local azurite and create your container
• In your application, add new parameter configuration to your relevant config/storage.yaml configuration: storage_blob_host: http://127.0.0.1:10000/devstoreaccount1
• Run application

[JoeDupuis]

Thank you for the contribution!
I made a couple changes to fix some shared access signatures issues and added public container creation to allow running the rails tests on azurite.

[JoeDupuis]

I'll cut a release shortly.