_redirects.yml is not kept when building documentation

I'm trying to use the new redirection feature with _redirects.yml in this PR: huggingface/optimum#441
The issue is that _redirects.yml does not appear anywhere in the generated documentation: https://github.com/huggingface/doc-build-dev/tree/main/optimum/pr_441/en

After taking a quick look, it seems to happen here:

doc-builder/src/doc_builder/commands/build.py

Lines 154 to 165 in e4cc563

    
           subprocess.run( 
        
               ["npm", "run", "build"], 
        
               stdout=subprocess.PIPE, 
        
               check=True, 
        
               encoding="utf-8", 
        
               cwd=working_dir, 
        
               env=env, 
        
           ) 
        
           # Copy result back in the build_dir. 
        
           shutil.rmtree(output_path) 
        
           shutil.copytree(tmp_dir / "kit" / "build", output_path)

The kit/build directory does not contain _redirects.yml, which is why it is not in the output directory when kit/build is copied there.

If the fix is simply to copy _redirects.yml to the output directory, I'm happy to open a PR. However, if we need to modify the configuration of npm I'm not sure I can help much.

@mishig25

	subprocess.run(
	["npm", "run", "build"],
	stdout=subprocess.PIPE,
	check=True,
	encoding="utf-8",
	cwd=working_dir,
	env=env,
	)

	# Copy result back in the build_dir.
	shutil.rmtree(output_path)
	shutil.copytree(tmp_dir / "kit" / "build", output_path)