Add ability to kill foreign query or session

[weres-sa]

There are some circumstances that require the possibility of interrupting a request sent in another session and/or by another user.

The most common case for such possibility is disaster recovery from system downtime caused by extremely inefficient query ran by mistake.

In oracle there is ALTER SYSTEM KILL SESSION clause, in postgresql - pg_cancel_backend function,
in cockroachdb -CANCEL QUERY clause.