feature/file: support multiple file selection

[dextermallo]

Is your feature request related to a problem? Please describe.

No. Have checked past issues/PRs and seems there's no relevant feature request.

Describe the solution you'd like

• Description: Adding multi-file selection (similar with gum choose) in the commnad gum file.
• Use cases: I would like to select multiple files as input for a command using gum file. The file paths are provided by users' inputs so I cannot use gum choose to define it.
• Implementation ideas: The logic of selection can be implemented the same as gum choose (

  gum/choose/command.go

  Line 80 in 0f8f67f

  currentSelected := 0

  ).

Describe alternatives you've considered

If files (that aims to be selected) are all under the same directory, gum choose solves the issues.

But it does not work when it comes to cross-directory (yes we can use -r to print the directory recusrively, but I think it's a mess :/)

Additional context

I am not a golang expert but I am willing to contribute :)