Add option to disable healthcheck for storagedriver in registry

From https://forum.gitlab.com/t/docker-registry-not-available/8049

It seems that registry generates 503 responses when the storage healthcheck fails, and the healthcheck fails when it is configured with an s3 backend that is empty.

Disabling the healthcheck is a workaround until #3381 (closed) is done.

Related to !2429 (merged)