Support `.config` dir for `devbox.json` and `process-compose.yml`

[eknowles]

What problem are you trying to solve?

Often root dir contain a mix of dot/env/config/lock files, these can make projects messy as ideally only critical files such as README or lockfiles would be in the root with configurations in .config.

What solution would you like?

Make location of devbox.json configurable via ENV var (envrc) and/or look for an alternative place if not in current dir such as ./.config/devbox.json

Alternatives you've considered

No response