get list of shell supported by module command

[xdelaruelle]

Seems interesting to get the list of shells supported by the installed module command.

A new state could be added to contain the list of shell currently supported by module.

Then a state sub-command could be added to list all defined states or a specific state if mentioned on the command line:

$ module state supported_shells
Modules Release 5.0.0+17-gbbab6f4a (2021-10-13)

- State name -----------.- Value ----------------------------------------------
supported_shells         sh bash ksh zsh csh tcsh fish cmd tcl perl python ruby lisp cmake r