Add new node with k6 for load tests, fixes #271

[evgeniiz321]

Yes, I tested it with an updated version of load test:

================================================================================================ test session starts =================================================================================================
platform linux -- Python 3.10.0, pytest-7.3.1, pluggy-1.0.0
rootdir: /home/ezayats/neofs-testcases/pytest_tests
configfile: pytest.ini
plugins: allure-pytest-2.9.45, lazy-fixture-0.6.3
collected 1 item

pytest_tests/testsuites/load/test_load.py::TestLoad::test_custom_load[1-4-grpc-1-4-200-200-0-0-1000-1mb_200.json] PASSED                                                                                       [100%]```