Cache driver GetBlob() allows read access to any blob without access control check

zot is an OCI image registry. Prior to 2.1.0, the cache driver GetBlob() allows read access to any blob without access control check. If a Zot accessControl policy allows users read access to some repositories but restricts read access to other repositories and dedupe is enabled (it is enabled by default), then an attacker who knows the name of an image and the digest of a blob (that they do not have read access to), they may maliciously read it via a second repository they do have read access to. This attack is possible because `ImageStore.CheckBlob()` calls `checkCacheBlob()` to find the blob a global cache by searching for the digest. If it is found, it is copied to the user requested repository with copyBlob(). The attack may be mitigated by configuring "dedupe": false in the "storage" settings. The vulnerability is fixed in 2.1.0.