fix(jellyfin): change cache to ephemeral storage

Using Memory apparently doesn't work anymore,
getting an error message:
`System.InvalidOperationException: The path  has insufficient free space. Required: at least 2GB.`

Signed-off-by: Vegard Hagen <vegard@stonegarden.dev>

k8s/apps/media/jellyfin/deployment.yaml

@@ -63,7 +63,6 @@ spec:
             server: 192.168.1.117
             path: /mnt/pool-0/data/media
         - name: cache
-          emptyDir:
-            medium: Memory
+          emptyDir: { }
         - name: tmp
           emptyDir: { }