[Feature]: Support viewing served files via `/rsbuild-dev-server` route

[9aoy]

What problem does this feature solve?

When the product writes to memory (execute rsbuild dev), it is difficult to find out which files were generated and what their paths are.

What does the proposed API look like?

like webpack-dev-server, visit /rsbuild-dev-server route will show where files are served. For example, http://localhost:3000/rsbuild-dev-server.