Remove @notblank annotations from CreateBookRequest

Removed @notblank annotations from several fields in CreateBookRequest.

Author: jimmy0006

src/main/java/org/poolc/api/book/dto/request/CreateBookRequest.java

@@ -22,27 +22,21 @@ public class CreateBookRequest {
     @Size(max = 100)
     private String author;
 
-    @NotBlank
     @Size(max = 100)
     private String publisher;
 
-    @NotBlank
     @Size(max = 100)
     private String isbn;
 
     private String description;
 
-    @NotBlank
     @Size(max = 100)
     private String pubdate;
 
-    @NotBlank
     private String image;
 
-    @NotNull
     private Integer discount;
 
-    @NotBlank
     private String link;
 
     @Size(max = 100)