Add option to avoid calling `cachix use`

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This is particularly useful on self-hosted runners where we can already add the Cachix cache to substituters but don't want to set the runner as a trusted user.

The better fix would've been to update cachix use to check if the substituters already contains the binary cache we're about to add, but I'm not too familiar with Haskell so this was the easiest way to fix this issue

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@domenkozar can you take a look at this when you have a chance?