Handle `nx` in sourcemaps wizard

[lforst]

From internal support ticket where the customer had trouble setting up source maps:

the confusion was due to the sentry wizard adding " devtool: 'source-map'" to our webpack config, instead of adding "sourceMap: true". as described in https://nx.dev/nx-api/webpack/executors/webpack#sourcemap

We should have a flow for the Nx webpack executor (or whatever it's called)