dev mode does not follow webpack output

Even if we override the webpack `output.filename` or `output.path`, the command `electron-webpack dev` will still try to load the `dist` directory for `main/main.js`. I think it should also try to run the output file from the persisting webpack config, after overrides.

In my case I configured the output to `build/tmp` since that has been the directory structure for almost all of the node apps. I used this method for overriding: [Modifying Webpack Configurations](https://webpack.electron.build/modifying-webpack-configurations)

Start at the electron-webpack dev command and trace how it selects dist/main/main.js after webpack configuration overrides. Reproduce the issue with output.filename or output.path set to build/tmp, then verify that the configured output file is loaded instead of the default dist path.

Written by the indexing model from the issue text.