Mark or filter out episodes only available to GO+ subscribers

[lebeno]

Is your feature request related to a problem? Please describe.
As described in #378, an episode fails to launch when it is not yet available for regular VTM Go subscribers, only for VTM GO+ subscribers. When browsing the episodes, all of them are listed, including a thumbnail. The only difference is that the episodes exclusively available to GO+ subscribers do not yet have a caption/description. It is very easy to miss this and when trying to launch such an episode, it fails to launch with a generic error.

Describe the solution you'd like
Assuming it is technically possible to determine GO+ subscription status: show the GO+-only episodes when the VTM GO account has such a subscription. Do not show these episodes when the account has no such subscription.
If is is not possible to determine the GO+ subscription status of the VTM GO account: add an option to the plugin settings: Do not show GO+ exclusive content.

Additional context
Regular episode:

GO+ exclusive episode showing thumbnail but no caption/description:

[KrSi78]

Just experienced the same issue but with older seasons of De code van Coppens. Only the latest season is available, the older produce the generic error. When browsing to the failing URL, a 426 - Upgrade Required error is returned.
When watching using an internet browser, one is informed visually that this episode is only for VTM GO+:

[davidbe]

I've been digging around a bit in the code and the json-responses. When using the browser, the picture of the show is shown with an overlay (for VtmGO+ or Streamz). This url is also retrieved from a get-request. If there is no overlay (so playable for everyone) the field is empty. Maybe that can be used and added to the titles?

For example, for De Acht Bergen (https://www.vtmgo.be/vtmgo/de-acht-bergen~dfbbc2de-4ab0-47e9-9bcf-32b6bf0f5128) the json returns (not a real json - it is already parsed):

"blockedFor" = NULL
"comingSoon" = NULL
"imageUrl" = "https://images3.persgroep.net/rcs/dhs_xSS-Pif8puoyGP-gaX77PuQ/diocontent/233469272/_fitwidth/320?appId=038a353bad43ac27fd436dc5419c256b&quality=0.8"
"overlayImageUrl" = "https://lfvp-static-overlays.dpgmedia.net/3/242844598"
"target" = #<HASH-TABLE :TEST EQUAL :COUNT 3 {1006122AF3}>
"title" = "De Acht Bergen"

The overlayImageUrl is the Streamz logo which is shown in the browser.

Colombiana (https://www.vtmgo.be/vtmgo/colombiana~ad97e552-5303-49ff-a3c5-4ccc55a9419b) is viewable and the overlayimageurl is empty:

"blockedFor" = NULL
"comingSoon" = NULL
"imageUrl" = "https://images0.persgroep.net/rcs/z7uMZUtVLbQimgJKPVRo6xoIUHI/diocontent/244789930/_fitwidth/320?appId=038a353bad43ac27fd436dc5419c256b&quality=0.8"
"overlayImageUrl" = NULL
"target" = #<HASH-TABLE :TEST EQUAL :COUNT 3 {10061255B3}>
"title" = "Colombiana"