Enforce/encourage coarser mags when annotating large volumes

[philippotto]

Detailed Description

Currently, users can restrict a volume annotation to certain magnifications, but most users don't know about this. When annotating large areas in mag 1, this puts a lot of strain on frontend/backend (long waiting time etc).
One idea is to emit a warning in the frontend when many updateBuckets are sent to the server. Ideally, user interactions that cause updates to large areas would be discarded in the first place. Maybe the upsampleVoxelMap code could have a limit that throws an error?

Context

• Specific to long-running jobs (set jobsEnabled=true in application.conf)
• Specific to webknossos.org (set isDemoInstance=true in application.conf)

[daniel-wer]

We could offer the option to delete some of the finest mags from the respective volume layer once this limit is hit. @fm3 maybe you can comment on the feasibility of that?

[daniel-wer]

With this issue, the brush preview bug in #8782 becomes more relevant

[fm3]

delete some of the finest mags

Yes, this could work. This would then only apply to the annotation versions starting from that updateMagList action, but that might be ok. Also we’d need to be careful in operations that stream all buckets (e.g. download, merge) to skip those buckets that are stored but are no longer in the mag list. Same for revert.