Add new public option for containers

[dadoonet]

When we create a container using Java API, we can easily make it public:

BlobContainerPermissions containerPermissions = new BlobContainerPermissions();
containerPermissions.setPublicAccess(BlobContainerPublicAccessType.CONTAINER);
container.uploadPermissions(containerPermissions);

So we could add an option to the repository such as "public": true (default to false), so people would be able to share their data using a public read-only URL.

[dadoonet]

Closing as living now at elastic/elasticsearch#12450