Add support for multiple executables

As a developer I would like to add support for running multiple executables from the same script using Tmux split

No file, test, or entry point is named. Start by tracing how LinuxGSM scripts launch executables and identify where Tmux sessions or splits are currently handled. Define the expected behavior for multiple executables and verify it with a representative game-server script.

Written by the indexing model from the issue text.