steam-remote: Add a stub steam executable
This stub steam executable tries to directly pass the given commands, e.g. "steam://nav/downloads", to the running Steam client.
This helps games that tries to run "steam ${command}" because when we are in a LD_LIBRARY_PATH runtime, "steam" might not be pointing to the same version that is currently running. Or if we are in a container, there is no "steam" executable in the PATH at all.