Upload nitro sourcemaps automatically in the SolidStart SDK

The `sentrySolidStartVite` plugin uploads sourcemaps generated during the vite build process, but not for the final nitro build step that generates the actual deployable output.

Nitro sourcemaps are referencing sourcemaps in the vinxi build folder, e.g `... "sources":["../../../../.vinxi/build/server-fns/_server/client-error.mjs"]`

We need to upload sourcemaps for both steps.