jstests/libs/os_helpers.js is now owned by Server Security, but that directory is full of various files owned by different teams. To keep files more organized, we should create a new directory called jstests/libs/server_security/ and move os_helpers.js in there. The new jstests/libs/server_security/ directory should have its own OWNERS.yml file that indicates all files within it are owned by the Server Security team.