Catalogue trainers: expanding search bar

[croml]

momenteel kan je wel zoeken op boektitel, maar dit willen we uitbreiden naar auteur, beschrijving/tags, ISBN

[iKerolos]

• Modified the SearchBookDto class to include a searchTerm field along with its getter and setter methods. This field represents the single search term entered by the user.
• Updated the searchBooks method in the backend service to utilize the searchTerm for searching books based on title, authors' names, and descriptions simultaneously.
• Implemented a Specification to construct the query dynamically, combining conditions for title, authors, and description using logical OR operations.