Don't require a specific script extension when running script from command prompt

[PascalLemieuxS]

Is your feature request related to a problem? Please describe

When running OpenToonz from windows command prompt, filePath argument can accept a path to a scene file or a script to be run, but for the script to be executed the it require a very specific extension - ".toonzscript" - which I saw nowhere in the documentation. In fact, from toonzscript documentation the only exemple of extension used is ".js". I think it's confusing and there is no good reason to be limited to this specific extension or to not mention this requirement in the help function of OpenToonz.exe

Describe the solution you'd like

Add a note to tell the required script extension is ".toonzscript" in the -help function of OpenToonz.exe or allow any extension that is not a scene file: ".tnz".