[add] Print messages about actions taken, or not taken.

[savil]

Summary

@Lagoja pointed out that devbox add <existing package> would exit with a no-op.

In this PR, I print messages during the execution of devbox add about changes made to each package.
If no changes were made for a package, then I explicitly print that at the end.

How was it tested?

# Add new package
> devbox add vim
Adding package "vim@latest" to devbox.json

Installing package: vim@latest.

[1/1] vim@latest
[1/1] vim@latest: Success
Recomputing the devbox environment.

# Add --platform to existing package
> devbox add vim --platform x86_64-darwin
Package "vim@latest" already in devbox.json
Added platform x86_64-darwin to package vim@latest

# Add multiple existing packages
> devbox add vim go@1.19.8
Package "vim@latest" already in devbox.json
Package "go@1.19.8" already in devbox.json
Packages vim@latest, go@1.19.8 were already in devbox.json and were not modified

# Add a mix of existing and new packages
> devbox add vim go@1.19.8 fzf
Package "vim@latest" already in devbox.json
Package "go@1.19.8" already in devbox.json
Adding package "fzf@latest" to devbox.json

Installing package: fzf@latest.

[1/1] fzf@latest
[1/1] fzf@latest: Success
Recomputing the devbox environment.
Packages vim@latest, go@1.19.8 were already in devbox.json and were not modified

[savil]

Current dependencies on/for this PR:

• main
  • PR [add] Print messages about actions taken, or not taken. #1527 👈

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[mikeland73]

Can we use ux.FInfo? I feel like these messages are important enough.