Add a script to list which local-override files exist

[kergoth]

I have hooks in a number of my configs to allow for local only changes, such as ~/.zshrc.local and ~/.gitconfig.local., but this means they're hidden from the dotfiles by design, so it'd be nice to have a way to see them on demand, in case any contain anything which is a candidate to fold into managed dotfiles, and also to ensure I don't forget they exist and are impacting my tool behavior.

Adding these to chezmoi-diff-managed as comparisons vs /dev/null` could be a viable way to expose them as additional types of "local system state that differs from managed dotfiles".

Related:

• chezmoi-diff-managed
• chezmoi unmanaged
• Create a systematic way to review system vs dotfiles differences #109

[kergoth]

This could potentially be another candidate of systematic local state vs managed state comparison per #109:

Existing:

• Local GUI application installations (if separate, as on a Mac)
• Local CLI tool installations (or binaries in ~/.local/bin, etc)

Exists as a script, but not part of #109 yet:

• Changes to merged managed state (chezmoi-diff-managed)

Proposed new section for #109:

• (This issue) Changes applied to tool configuration via overlays

[kergoth]

I don't think this should fold into chezmoi-diff-managed, because chezmoi-diff-managed is shaped like chezmoi diff, and I think it should keep that shape. It's essentially "chezmoi diff without existing state in the mix", which is a different category of tool than "compare my current tool configurations to managed", and the latter fits the definition of the proposed #109 tooling.