NCBACK-25 add protection for audio and use hash method from library

src/main/java/ru/soune/nocopy/entity/file/FileEntity.java

@@ -76,6 +76,10 @@ public class FileEntity {
     @Column(name = "protected_at")
     private LocalDateTime protectedAt;
 
+    @Column(name = "signature")
+    @JsonIgnore
+    private String signature;
+
     @OneToOne(mappedBy = "file", cascade = CascadeType.ALL, orphanRemoval = true)
     @JsonIgnore
     private ImageHashEntity imageHash;