Allow to filter upcoming cards

At Nextcloud we use Deck a lot. This means that I not only have my own boards but many boards shared from colleagues. Many of them are just shared with me "for my information" or for occasional collaboration. But the board fills up my "upcoming card" view with so many cards up to come and overdue cards that I can't use it to keep an overview over my boards and the cards and due dates I really care about.

Possible solution:

1. Filter option on "upcoming cards" so that I can hide the boards I don't care. Filter should remember the last setting so that I don't have to apply the filter again and again.
2. Introducing a setting per board and user, similar to the "due date reminder" setting, allowing the user to define board by board if it should show up in the overview or not
3. Reuse the existing "due date reminder" setting and assume that when people don't want to get notifications for boards, they also don't want to see the cards on "upcoming cards" as they don't care about the deadlines.

Start by locating the upcoming cards view and the existing per-board due date reminder setting. Compare the three proposed approaches and confirm the intended behavior with maintainers before choosing an entry point. Done means users can exclude selected boards from the overview and the choice persists as specified.