refactor(newsletter): ♻️ Media servers + newsletter refactoring (#4463)

* Abstract media servers content into interfaces

* Media server entities into abstract classes

* Abstract media server content repository

* First pass at newsletter refactoring

* Minor code clean up

* Attempt at abstracting repositories (WIP)

* Fixed cast issue

* Corrected the other properties

* A step towards newsletter refactoring

* Clean up leftovers

* Fix broken episodes db interaction

* Save absolute URL for Plex content

Let's be consistent with Emby and Jellyfin

* Fix broken integration with Plex libraries

* Fix error when multiple media servers configured

* Fix newsletter being sent if no movies or episodes

* Fix broken tests

* Remove unneccesary logs

* Expose stored media server URL

No need to recalculate it
+ Plex URL was broken due to an earlier change

* Remove unused variable

* Remove obsolete tests

URLs are now fetched from database directly

* Retro-compatibility for Plex content URL

Solves URL for media synced before absolute URL was saved in PlexServerContent

* chore: added some obsoletes

* fix: removed the unsub link when not present

Co-authored-by: tidusjar <tidusjar@gmail.com>

src/Ombi.Store/Repository/IExternalRepository.cs

@@ -9,7 +9,7 @@ using Ombi.Store.Entities;
 
 namespace Ombi.Store.Repository
 {
-    public interface IExternalRepository<T> where T : Entity
+    public interface IExternalRepository<T> where T : IEntity
     {
         Task<T> Find(object key);
         IQueryable<T> GetAll();
@@ -25,6 +25,5 @@ namespace Ombi.Store.Repository
             where TEntity : class;
 
         Task ExecuteSql(string sql);
-        DbSet<T> _db { get; }
     }
 }