Implement /FCLEAN

[akaszynski]

Description of the feature

Based on the discussion in #1604, I think it would be great to expose /FCLEAN. I didn't even realize that this command existed!

We might want to consider being like Mechanical and making this a default, but then we'll conflict with the existing remove_temp_files, which removes all MAPDL files, which seems more like a black/white solution rather than /FCLEAN, which seems like a sensible default.

Steps for implementing the feature

Add /FCLEAN and example to our commands.

Useful links and references

Only public reference with reasonable information is and the above discussion https://forum.ansys.com/forums/topic/delete-unneded-files-in-apdl/

Thanks for pointing this out @mikerife