Fix v1 config error propagation

[fibonacci1729]

When updating to variables I implemented the spin_world::v1::config::Host trait in terms of the variables::Host implementation. However (and i'm not sure how/why) the variables::Error (defined in variables.wit) was being propagated back to the ABI and causing a panic deep in the bowels of something. In any case, i decided to simply remapvariables::Error to a variant in spin_world::v1::config::Error which appears to correct the issue.

[itowlson]

Thanks! Worth testing with the redirect component if you've not already done so?

[fibonacci1729]

@itowlson have done so and no error so seemingly fallback kicks in as expected.

[itowlson]

@fibonacci1729 merged this because Karthik's bartholomew build hit it too, hope that's okay