devices: add group for devices with only 6M flash

[grische]

Currently, 6M flash is not sufficient to build the default firmware on some communities. This allows filtering for those devices.

[grische]

As discussed here, adding the DIR-825 back to the recommended list: freifunk/meshviewer#75 (comment)

[herbetom]

Problem with adding a new category is that devices will be always hidden for existing Users without them adjusting their config and it isn't a opt-in. Those models won't even be selectable via the "only show recomended" feature (if enabled) without enabling them first.

Not all of those devices will be dropped in the upcoming Gluon v2023.2. I haven't checked but would therefore suspect not all of them share the same exact limit.

I would probably prefer allowing 6m devices beeing selectable via some major change that completly rethinks how devices are added. Or having some "don't advertise"/"hide devices" list via the config to allow communities to hide what they thing should be hidden.

But I haven't thought it all through and I don't want to be nailed down to thinking those would be good approaches 🙈