sse-c: use different object encryption key for each object

src/api/s3/encryption.rs

@@ -69,9 +69,9 @@ pub enum EncryptionParams {
 		client_key: Key<Aes256Gcm>,
 		/// the value of x-amz-server-side-encryption-customer-key-md5
 		client_key_md5: Md5Output,
-		/// the object encryption key
+		/// the object encryption key, for uploads created in garage v2+
 		object_key: Option<Key<Aes256Gcm>>,
-		/// the compression level for data blocks (not relevant for header)
+		/// the compression level used for compressing data blocks
 		compression_level: Option<i32>,
 	},
 }