feat: CLI app for getmud module

[yucongalicechen]

Problem

We want to have CLI command for getmud module.
Some previous progress can be found in #184

We should maybe discuss what the CLI should look like. Are they separate apps that do those tasks, or do we want one entry point but give different behavior if different command line switches are used? For example, for UC1 should the user type get_diameter <composition> <energy> <mass-density> or do we want them to type something like labpdfproc --get-d <composition> <energy> <mass-density> or sthg else?

Originally posted by @sbillinge in #175 (comment)

[yucongalicechen]

Closing this as we'll open new issues for the getmuD CLI apps. The example here (UC1) has been decided not to be implemented (see #166).