Add PATH configuration for fish shell

[lytedev]

- Summary

fish shell users are unable to run netlify lm:install or netlify lm:setup successfully. This change enables the plugin to function when running inside fish.

- Test plan

I made this change, ran netlify plugins:link, then my LFS setup worked (as tested via git push and seeing the LFS objects get pushed up).

- Description for the changelog

Add PATH configuration for fish shell

- A picture of a cute animal (not mandatory but encouraged)

Here's a potato-quality picture of my cat:

[erezrokah]

Thanks @lytedev, just a heads up as we are merging this repo into Netlify CLI:
netlify/cli#1489.

Going to keep this one open until netlify/cli#1489 is merged.

[erezrokah]

Closing in favor of netlify/cli#1943.
@lytedev do you mind having a look at that one?