Expose AzureBlobStorageContainer block at top level to ensure it is…

… registered with Prefect's ojbect registry (#145)

#Please enter the commit message for your changes. Lines starting

prefect_azure/__init__.py

@@ -7,6 +7,7 @@
 )
 from .workers.container_instance import AzureContainerWorker  # noqa
 from .container_instance import AzureContainerInstanceJob  # noqa
+from .blob_storage import AzureBlobStorageContainer  # noqa
 
 __all__ = [
     "AzureBlobStorageCredentials",
@@ -15,6 +16,7 @@
     "AzureContainerInstanceCredentials",
     "AzureContainerInstanceJob",
     "AzureContainerWorker",
+    "AzureBlobStorageContainer",
 ]
 
 __version__ = _version.get_versions()["version"]