Per-space setting to include DMs in notification count

### Your use case

#### What would you like to do?
I would like the option (back in an improved way) to show DM notifications in the space notification counter (the grey bubble 1 seen here on the white home space).


I realize that a conscious decision was made to remove not only DM notifications but also the global toggle from spaces settings. As far as I know, the main reason was that DMs would potentially light up many spaces. I ask you to reconsider and add it back in the following modified way which tries to either prevent that or does it on purpose and only when selected, without stripping the feature completely.

#### Why would you like to do it?
In this case I have a DM notification in the pink :house: space, which is a private space and includes some *manually* added DMs.

The problem here is that this behaviour is confusing to me, and frankly disrupted my workflow since the global toggle has been removed. I added DMs purposefully to this space, so I would naturally expect them to be included here. The badge being only on the home space suggest that this notification is explicitly *not* in a space.

This behaviour renders adding DMs to personal spaces half useless in my opinion.

#### How would you like to achieve it?
Add back the option to count DMs into space notifications, but with a toggle per space.

### Have you considered any alternatives?

It might make sense to allow these only for
- personal spaces, because the DMs were purposefully added by me and so I expect the notification count. Perhaps the proposed toggle should even default to enabled here.
- private spaces, because all members are a (closed) community and so you can reasonably expect context here.

I don't really see a downside in offering it also for public spaces, especially as long as DMs are automatically included in public spaces which is questionable in itself.

### Additional context

I am sure there are lots of closed and open issues regarding spaces and DMs as well as spaces and notifications.