Project: webpack
Task (challenging): I want to do something with sourcemap files in output directory.
Implement this as a local webpack plugin.

## Requirements
- Move all sourcemap files into `<project_root>/sourcemaps` after build.
- Add `//# sourceMappingURL=https://internal.com/sourcemaps/<sourcemap_path>` at the end of original js file.

## Examples
Assume we have following files in dist directory before moving:
- dist/assets/index.js
- dist/assets/index.js.map
- dist/assets/index.css
- dist/assets/index.css.map

After moving, the files should be:
- dist/assets/index.js
- dist/assets/index.css
- sourcemaps/assets/index.js.map
- sourcemaps/assets/index.css.map

And the `dist/assets/index.js` should contain the following content at its end(Using JS comment):
//# sourceMappingURL=https://internal.com/sourcemaps/assets/index.js.map

And the `dist/assets/index.css` should contain the following content at its end(Using CSS comment):
/*# sourceMappingURL=https://internal.com/sourcemaps/assets/index.css.map */