fix: remove non-null requirement for some fields (#1175)

PR #628 changed some fields to disallow null values, causing issues with some older SQLite database
having null values. This PR reverts this change.

server/entity/MediaRequest.ts

@@ -385,7 +385,6 @@ export class MediaRequest {
   @ManyToOne(() => Media, (media) => media.requests, {
     eager: true,
     onDelete: 'CASCADE',
-    nullable: false,
   })
   public media: Media;
 

server/entity/Season.ts

@@ -25,7 +25,6 @@ class Season {
 
   @ManyToOne(() => Media, (media) => media.seasons, {
     onDelete: 'CASCADE',
-    nullable: false,
   })
   public media: Promise<Media>;
 

server/entity/Watchlist.ts

@@ -53,7 +53,6 @@ export class Watchlist implements WatchlistItem {
   @ManyToOne(() => Media, (media) => media.watchlists, {
     eager: true,
     onDelete: 'CASCADE',
-    nullable: false,
   })
   public media: Media;