Container default access level possible security issue for Umbraco Forms

[AstuteMediaDev]

Related to #67 and #98

there is a hard-coded use of BlobContainerPublicAccessType.Blob when creating the container.

Umbraco Forms uploads files to /media/forms and we only just realised the default container access is public so anyone could potentially access sensitive user uploads if they were aware of the storage account url.

[JimBobSquarePants]

We have other options now. It's not hard coded since #64

It's also documented.

https://github.com/JimBobSquarePants/UmbracoFileSystemProviders.Azure#usage

Protecting the media by default changes the default behaviour from the file based service and requires ImageProcessor.Web customization.