I don't intend fully on getting this merged, this is just an experiment
on using `direnv` directly without relying on shell-specific behaviours.
It works though, so this finally closes #8633
Release Notes:

- Fixed nushell not picking up `direnv` environments by directly
interfacing with it using `direnv export`

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Co-authored-by: Thorsten Ball <mrnugget@gmail.com>