Add a Radarr feed URL for watchlist sync

[JVT038]

The radarr feed URL works similar to the webhook URLs.

The URL looks like localhost/api/radarr/<UUID> and the UUID is stored in the users table.

The URL responds with a JSON list of all the watchlist items. It looks like this:

[
    {
        "title": "ThanksKilling",
        "tmdb_id": 60366,
        "imdb_id": "tt1129441",
        "added_at": "2023-05-20 20:37:30"
    },
]

The user can add this list quite easily by going to Radarr, add it as a custom StevenLu list and enter the feed URL from Movary.

[leepeuker]

We should add the new radarr integration to the docs