Add Option to configure "Up Next" behaviour

[t0815]

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Feature Description

Currently, if a show has unwatched specials, they are treated the same as unwatched regular episodes. But most of the time, this specials are just small little extras, not really worth watching. It would be cool, if we could configure the up-next and unwatched episodes behaviour, if specials should be included in this state or not.

Feature Examples

Maybe add a general option, if the user wants to include specials to count towards unwatched episodes count state.

[revam]

web ui can already control this if they want. moving issue.

https://github.com/ShokoAnime/ShokoServer/blob/master/Shoko.Server/API/v3/Controllers/SeriesController.cs#L2249-L2303

[hidden4003]

Hardest part of this is deciding where to put the actual option, we don't really have settings menu for this unless we use dashboard settings.

[t0815]

I think, dashboard settings makes the most sense, yes.