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

As reported in earlier issues, I'm experimenting with chezmoi to run as root to manage my / folder at felipecrs/dotfiles#44. I'm already able to force chezmoi to use my own config file and persistent state with the cli flags, but I would also like to be able to specify a custom cache dir to use instead of ~/.cache/chezmoi, because otherwise, cache would be written to /root/.cache/chezmoi, where I would prefer them to be stored under some place like /home/felipecrs/.cache/rootmoi.

That's because I'm not running chezmoi as root because I'm root, but because I want chezmoi to do some rootful operations on behalf of me.

I would not like to mix the cache of intentional use of root user with chezmoi with mine.

Describe the solution you'd like

A new global flag --cache-dir, which would allow me to set a different cache directory for chezmoi to use.

Describe alternatives you've considered

To live with the default despite the caveats mentioned.

Additional context

None.