When using permissions that use tags, a user may receive multiple permissions
of the same type if multiple tags are assigned to the device. This causes the
RestrictedQuerySet class to generate a query similar to this:
>>> dcim.models.Device.objects.filter(Q(tags__name='tag1')|Q(tags__name='tag2'))
<ConfigContextModelQuerySet [<Device: device1>, <Device: device1>]>
This query returns the same object twice if both tags are assigned to it. This
is due to the use of the django-taggit library. The library's documentation
describes this behavior as expected and suggests using an explicit distinct()
call in queries to avoid duplicates.
However, the use of DISTINCT in queries has a global side effect -
deduplication of responses, which may or may not be acceptable behavior
(depending on further use). Since it is not known how RestrictedQuerySet will
be used in the rest of the code, it was decided to dedupe using a subquery.
