Fix Jellyfin library access for new users

[EthanArmbrust]

Fixes #101

[realashleybailey]

I have approved this as it looks okay and works, is it possible if you could explain your process as to why you believe this change fixes the bug so we can have a record for it when we come around to rewriting this code for Wizarr V3

[EthanArmbrust]

I put a little comment explaining it in the review. I've tested it my personal jellyfin server to confirm that it works.

[EthanArmbrust]

My review shows as pending so I'll put it here too.

https://github.com/Wizarrrr/wizarr/blob/771c3f128959da497867ef9888ff3513579a860d/app/jellyfin.py#L66
This line overwrites the two existing values that we want in policy with the jellyfin defaults from the GET response. We need to update the response's dict with our policy , not update our policy with Jellyfin's response. Then we can post the updated policy.