Add default/local option

[wpbonelli]

The action is currently network-dependent. All three runner images come with gfortran (windows via mingw), it would be nice to have an option to use the pre-installed one. E.g. bool "local" overriding any compiler/version selection.

[wpbonelli]

brew/apt are lazy so nothing to do on linux/mac, maybe update windows to avoid reinstalling major versions

#49 updates logic for apt, brew and choco to only install if needed