OPDS-PS v1.2 Support + a few bugfixes (#1869)

* Fixed up a localization lookup test case

* Refactored some webp to a unified method

* Cleaned up some code

* Expanded webp conversion for covers to all entities

* Code cleanup

* Prompt the user when they are about to delete multiple series via bulk actions

* Aligned Kavita to OPDS-PS 1.2.

* Fixed a bug where clearing metadata filter of series name didn't clear the actual field.

* Added some documentation

* Refactored how covert covers to webp works. Now we will handle all custom covers for all entities. Volumes and Series will not be touched but instead be updated via a RefreshCovers call. This will fix up the references much faster.

* Fixed up the OPDS-PS 1.2 attributes to only show on PS links

API/DTOs/ProgressDto.cs

@@ -1,4 +1,5 @@
-using System.ComponentModel.DataAnnotations;
+using System;
+using System.ComponentModel.DataAnnotations;
 
 namespace API.DTOs;
 
@@ -19,4 +20,6 @@ public class ProgressDto
     /// on pages that combine multiple "chapters".
     /// </summary>
     public string? BookScrollId { get; set; }
+
+    public DateTime LastModifiedUtc { get; set; }
 }