[Feature Request] `killOp` command

[AlekSi]

Purpose of the feature.

#52 fixed $currentOp aggregation pipeline stage. It would be nice if DocumentDB also provided a safe way to stop the operation – killOp command.

Describe the solution you'd like

DocumentDB implements killOp command.

Describe alternatives you've considered

Implement it in FerretDB (somehow).

Additional context

N/A.