Multiple "assigned to" filters at the same time

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Is your feature request related to a problem? Please describe.
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I am working in an IT Department of a medium-sized Business, and we use deck for our Task and priority planning. Every user puts in their tasks and assigns it to himself.

Sometimes we create tasks with no user assigned at the time, and then I usually don't see it, because I always have the filter set on only my tasks.

Describe the solution you'd like
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It should be possible to select one user as well as the unassigned or another user tag when filtering by "Filter by assigned user". That way you can see both the tasks assigned to you and the unnassigned ones

Describe alternatives you've considered
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Don't use a Filter, but that gets messy quickly.

Additional context
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The issue names no files or tests. Start by tracing Deck's “Filter by assigned user” entry point and its handling of selected assignees; done means the filter can show tasks assigned to the current user together with unassigned tasks or another selected user.