Add a possibility to add error injections to the code from system tests

For tests like these - https://github.com/nspcc-dev/neofs-testcases/issues/794 we need a way to put the system under the test to certain conditions that can't be easily and reliably reproduced under regular circumstances, but we can encounter them running the production code.

The most convenient thing from the test perspective would be the possibility to add error injections to some code places. E.g. if we want to get an unfinished object and want to validate how it is cleaned, it would be nice to inject an error during the object creation operation and got such an unfinished object.

Same feature could be also applied to verify more unusual scenarios and different states of the system. To ensure the robust recovery from other possible faulty situations.

I would expect it to be implemented either via env variables/config files before service starts, or, more conveniently via some internal cli commands - like ./neofs-cli inject-error ERROR_LOCATION ERROR_TYPE, where ERROR_LOCATION is a specific place in the code and ERROR_TYPE is either a panic, or a sleep with different number of seconds, or a bool value that somehow is used in the code. E.g.
./neofs-cli inject-error OBJECT_CREATION_POST_PARTS_CREATE RETURN_FALSE

Start by reviewing the linked neofs-testcases issue and the existing neofs-cli command entry points. Define the supported injection locations and behaviors before choosing configuration or CLI control; done means system tests can reliably trigger the requested failure states and validate recovery.